Free BMI +
Calorie Calculator
Instantly calculate your BMI and daily calorie needs for weight loss, maintenance, or muscle gain.
BMI Calculator
Calculate your Body Mass Index for men, women, kids & teens. Includes healthy weight range, BMI Prime & reverse lookup.
Free BMI Calculator — Men, Women, Kids & Teens
BMI Calculator
Calculate your Body Mass Index instantly — for men, women, kids, or teens — with metric or imperial units, your category, healthy weight range, BMI Prime, and a reverse BMI lookup to find your target weight.
Which calculator should you use? Use the Adult Calculator to calculate BMI for a man or woman aged 20 or older — adult BMI is read against fixed cutoffs regardless of age or sex. Use the Kids & Teens Calculator for a child, pediatric, or teen BMI between ages 2–19 — kids' BMI is judged against age- and sex-specific growth percentiles instead. Use the Reverse BMI Calculator if you already know the BMI you're aiming for and want to find the target weight for your height. Picking the wrong one will give a misleading category.
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BMI is a general screening measure and does not directly assess body fat or account for muscle mass, frame size, age, or sex. Consult a healthcare professional for a full assessment.
What Is BMI (Body Mass Index)?
Body Mass Index (BMI) is a simple calculation using a person's height and weight. The formula is BMI = weight (kg) ÷ height (m)², or for imperial units, BMI = 703 × weight (lb) ÷ height (in)². It's used by doctors and health organizations — including the CDC and WHO — as a quick screening tool to categorize body weight into ranges that may indicate health risk.
How to Calculate BMI Step by Step
Wondering exactly how BMI is calculated? Here's the calculation broken into steps, whether you do it by hand or let the calculator above do it instantly:
- Measure your height and weight (metric or imperial — the calculator above handles both).
- Convert height into metres (metric) or stay in inches (imperial).
- Square the height value (multiply it by itself).
- Divide your weight by that squared height — for pounds and inches, multiply the result by 703 first.
- Compare the resulting number against the BMI category table below to see where you fall.
Worked example: someone who is 5 ft 10 in (70 in) and weighs 160 lb gets BMI = 703 × 160 ÷ 70² ≈ 23.0 — squarely in the healthy range.
BMI Categories for Adults
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Full Adult BMI Classification (WHO)
Public health bodies break the adult BMI scale into finer bands than the four broad categories above. The World Health Organization's full classification, used for both men and women aged 20 and over, is:
| Classification | BMI Range (kg/m²) |
|---|---|
| Severe thinness | Below 16 |
| Moderate thinness | 16 – 16.9 |
| Mild thinness | 17 – 18.4 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese class I | 30 – 34.9 |
| Obese class II | 35 – 39.9 |
| Obese class III | Above 40 |
BMI Calculator for Women
The BMI formula itself doesn't change for women — it's the same weight-over-height² calculation used for everyone. What changes is interpretation: at the same BMI, women on average carry a higher percentage of body fat than men, and factors like pregnancy, menopause, and hormonal changes can shift body composition without changing the BMI number itself. A BMI calculator for women is most useful as a starting screening point — pair it with waist circumference or a body fat reading for a fuller picture, and skip BMI tracking altogether during pregnancy, when weight gain is expected and healthy.
BMI Calculator for Men
For men, the same formula applies, but muscle mass is the bigger wildcard. Men tend to carry more lean muscle than women at an equivalent BMI, which is why muscular or athletic men — including many lifters and team-sport athletes — can land in the "overweight" BMI band while actually carrying low body fat. If you train seriously and your BMI looks high, a body fat percentage or waist-to-height ratio will usually tell a more accurate story than BMI alone.
BMI for Children and Teens (Ages 2–20)
BMI works differently for growing bodies. Instead of fixed cutoffs, the CDC places a child's BMI on an age- and sex-specific growth percentile, since "normal" body composition shifts constantly between toddlerhood and late adolescence.
| Category | Percentile |
|---|---|
| Underweight | Below 5th percentile |
| Healthy weight | 5th – 84th percentile |
| Risk of overweight | 85th – 94th percentile |
| Overweight | 95th percentile and above |
This calculator is built for adult screening. If you're checking a child's growth, compare their result against a pediatric BMI-for-age chart with your doctor rather than the adult categories above.
BMI Formula Reference
- Metric: BMI = weight in kilograms ÷ (height in metres × height in metres)
- Imperial: BMI = 703 × weight in pounds ÷ (height in inches × height in inches)
BMI Prime: How Far From the Healthy Ceiling?
BMI Prime takes your BMI and divides it by 25, the conventional upper edge of the "normal" band. The result is a clean ratio rather than a unit-based score, which makes it easy to see at a glance how far above or below the healthy ceiling someone sits, and makes comparisons across groups with different reference cutoffs simpler.
| Classification | BMI | BMI Prime |
|---|---|---|
| Underweight | Below 18.5 | Below 0.74 |
| Normal | 18.5 – 24.9 | 0.74 – 1.0 |
| Overweight | 25 – 29.9 | 1.0 – 1.2 |
| Obese | 30 and above | Above 1.2 |
Ponderal Index: A Better Fit for Very Tall or Short Bodies
The Ponderal Index (PI) works like BMI but cubes height instead of squaring it. Because BMI tends to skew unusually high or low for people at the extreme ends of the height spectrum, PI generally gives a more proportionate read for very tall or very short individuals, even though it shares most of BMI's other limitations.
Formula (metric): PI = weight in kg ÷ (height in metres)³
Health Risks Linked to Excess Weight
Carrying significantly more weight than the healthy range suggests is associated with a higher likelihood of several serious conditions, including elevated blood pressure, unfavorable cholesterol and triglyceride levels, type 2 diabetes, heart disease, stroke, gallbladder disease, osteoarthritis, sleep apnea, certain cancers, and a generally higher mortality risk compared with people in the healthy BMI range. It can also affect mental wellbeing and day-to-day mobility. Aiming to keep BMI under roughly 25, in consultation with a doctor, is a reasonable general target for most adults.
Health Risks Linked to Being Underweight
A BMI below the healthy range carries its own risks: nutrient deficiencies and anemia, weaker bones and higher fracture risk, reduced immune resilience, slower growth and development in children and teens, fertility complications and elevated early-pregnancy miscarriage risk in women, and a higher chance of complications during surgery. In some cases, persistent low weight signals an underlying condition, so it's worth discussing with a doctor rather than ignoring.
Where BMI Falls Short
BMI is a screening shortcut, not a diagnosis. It measures excess weight, not excess fat, so it can't tell the difference between muscle and fat mass. That means a heavily muscled athlete can register as "overweight" while carrying very little body fat, while an inactive older adult of the same BMI may carry more fat than the number suggests. Sex, age, ethnicity, and activity level all shift how much a given BMI actually reflects body composition — generally, older adults and women tend to carry more body fat than younger adults or men at the same BMI. Despite these caveats, BMI tracks reasonably well with body fat for the large majority of people, which is why it remains a useful first-pass indicator when paired with other measures like waist circumference, body fat percentage, or a doctor's assessment.
Reverse BMI Calculator: Find Your Target Weight
A reverse BMI calculator flips the usual question. Instead of "what's my BMI?", it answers "what would I need to weigh to reach a specific BMI?" Pick your height and a target BMI in the Reverse BMI tab above, and it works backward through the same formula to show the matching weight. This is a plain mathematical conversion, not a recommendation — what BMI is actually appropriate for you depends on your frame, muscle mass, age, and health history, so treat the result as a reference point to discuss with a doctor rather than a fixed goal.
Frequently Asked Questions
How is BMI calculated?
BMI is calculated by dividing weight by height squared: weight in kilograms ÷ (height in metres)², or 703 × weight in pounds ÷ (height in inches)². The calculator above does this instantly for either unit system.
Is BMI accurate for everyone?
BMI is a useful population-level screening tool, but it has limitations. It doesn't distinguish between muscle and fat, so very muscular people may show a higher BMI without excess body fat. It also doesn't account for bone density, body composition, or fat distribution, so it should be considered alongside other measures like waist circumference or body fat percentage.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered within the healthy weight range, according to standard World Health Organization classifications.
Is BMI calculated differently for men and women?
The formula is identical for both. The difference is in interpretation: women tend to carry more body fat than men at the same BMI, so the number means something slightly different for each sex even though the calculation doesn't change.
Does BMI differ for children, teens, or pediatric use?
Yes. For children and teens, BMI is interpreted using age- and sex-specific percentile charts rather than the fixed adult categories, since body composition changes throughout growth. Use the Kids & Teens tab above for ages 2–19.
What's the difference between BMI, BMI Prime, and the Ponderal Index?
BMI gives you a weight-to-height² score. BMI Prime expresses that same score as a ratio against the healthy ceiling of 25, which makes it easier to gauge how far someone is from that limit. The Ponderal Index uses height cubed instead of squared, which tends to be more proportionate for people who are unusually tall or short.
What is a reverse BMI calculator used for?
A reverse BMI calculator works the formula backward: instead of entering height and weight to get a BMI, you enter your height and a target BMI to find the matching target weight. It's a quick way to translate a BMI goal into an actual weight number.
How often should I check my BMI?
There's no strict rule, but checking every few months alongside other health markers can help you track trends over time rather than focusing on a single number.
Now that you know your BMI…
Calculate your daily calorie needs for weight loss or maintenance →Calorie Calculator
Find your daily calorie needs using Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle formulas.
Free Daily Calorie Calculator
Calorie Calculator
Find out how many calories you need per day to maintain, lose, or gain weight — based on the Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle equations.
"Lose 1 kg/wk" is close to the generally recommended upper limit for safe weight loss. We don't recommend going below this without medical supervision — and most people do better, longer-term, aiming for the 0.25–0.5 kg/week range.
These figures are estimates based on population-average formulas, not a personalized medical or nutrition plan. Actual needs vary with metabolism, body composition, and health conditions — consult a doctor or registered dietitian before making major changes to your diet.
How Many Calories Do You Need Per Day?
Your daily calorie need depends on your Basal Metabolic Rate (BMR) — the energy your body burns at complete rest just to keep your organs running — multiplied by an activity factor that accounts for movement and exercise throughout the day. This calculator estimates that number, then shows you the calorie targets for maintaining, losing, or gaining weight at a sustainable pace.
BMR Formulas Explained
This calculator can use any of three established equations, each with a slightly different approach:
- Mifflin-St Jeor (default): the formula most dietitians consider the most reliable for the general population today. For men: 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. For women: 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161.
- Revised Harris-Benedict: an older formula, refined in 1984, that's still widely used and reasonably accurate, though generally considered slightly less precise than Mifflin-St Jeor for most people today.
- Katch-McArdle: calculates resting daily energy expenditure based on lean body mass rather than total weight, which makes it more accurate for leaner or more muscular people — but only if you know your body fat percentage.
Activity Level Multipliers
Once BMR is estimated, it's multiplied by an activity factor to estimate total daily calorie burn (TDEE):
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Little to no regular exercise |
| Light | 1.375 | Light exercise 1–3 days/week |
| Moderate | 1.55 | Moderate exercise 4–5 days/week |
| Active | 1.725 | Daily exercise or intense exercise 3–4 days/week |
| Very active | 1.9 | Intense exercise 6–7 days/week |
| Extra active | 1.95 | Very intense daily training or a physically demanding job |
The Math Behind Weight Loss and Gain
A pound of body weight is roughly equivalent to 3,500 calories. So trimming about 500 calories a day from your maintenance level theoretically adds up to a 1-pound (≈0.45 kg) loss per week, and adding 500 calories a day theoretically supports about a pound of gain per week. Most health authorities recommend not cutting more than around 1,000 calories a day below maintenance, since losing more than roughly 2 pounds (≈1 kg) a week regularly risks muscle loss, a drop in metabolic rate, and rebound weight regain — talk to a doctor or registered dietitian before pursuing faster loss than that.
How Many Calories Do You Actually Need?
Daily calorie needs vary widely depending on age, weight, height, sex, activity level, and overall health — there's no single right number. As a rough guide, adult men generally need somewhere in the range of 2,000–3,000 calories a day to maintain their weight, while adult women typically fall closer to 1,600–2,400, according to general U.S. dietary guidance. Someone like an active 25-year-old man will sit toward the high end of that range, while a sedentary older adult will sit toward the low end — which is exactly why a personalized calculator like this one is more useful than a single generic number.
There's also a practical floor: cutting calories too aggressively backfires, since the body starts conserving energy for essential survival functions rather than supporting general health. As a general caution echoed by major health publications, women are typically advised not to dip below roughly 1,200 calories a day and men not below roughly 1,500, except under direct medical supervision.
Not All Calories Are Equal
Total calories drive weight change, but where those calories come from still matters for health and hunger. A few patterns worth knowing:
- The thermic effect of food: foods that take more effort to chew and digest — vegetables, lean meats, whole grains — burn slightly more calories during digestion itself and tend to keep you fuller longer than heavily processed foods.
- Empty calories: added sugars and certain fats provide energy with little nutritional value. Sugary drinks are a major source — beverages alone can account for roughly a fifth of a typical diet's calories.
- "High-calorie" isn't automatically "unhealthy": foods like avocados, nuts, and whole grains are calorie-dense but nutrient-rich, while some "low-fat" or "diet" products simply swap fat for added sugar.
- Portion size matters more than people realize: restaurant portions are often two to three times a standard serving, and something as simple as using a smaller plate has been shown to reduce how much people eat.
Zigzag (or "calorie cycling") is an approach where you vary your daily calorie intake — some higher days, some lower — while keeping the same weekly total as a steady daily deficit would produce. The idea is to avoid the body fully adapting to a constant lower-calorie environment, which can otherwise contribute to weight-loss plateaus. For example, instead of eating 2,000 calories every day to hit a 14,000-calorie weekly target, you might eat 2,300 calories on three days and around 1,775 on the other four — same weekly total, more flexibility for social occasions, and arguably less metabolic adaptation. There's no single proven "best" split; most people who use this approach vary high and low days by roughly 200–300 calories.
Sample Meal Plans (1,200 / 1,500 / 2,000 Calories)
Here's a rough sense of how a day's calories might be distributed across meals at three common targets — these are illustrative examples, not a personalized plan:
| Meal | ~1,200 cal/day | ~1,500 cal/day | ~2,000 cal/day |
|---|---|---|---|
| Breakfast | Cereal, milk, banana | Granola, Greek yogurt, berries | Toast, egg, banana, almonds |
| Lunch | Grilled cheese, side salad | Chicken & vegetable soup, bread | Grilled chicken, vegetables, pasta |
| Dinner | Grilled chicken, sprouts, quinoa | Steak, mashed potatoes, asparagus | Grilled salmon, brown rice, green beans |
| Snacks | Cucumber & dip, orange | Yogurt & berries | Walnuts, peanut butter, crackers |
Calories in Common Foods (Quick Reference)
| Food | Serving | Approx. Calories |
|---|---|---|
| Apple | 1 medium | ~60 |
| Banana | 1 medium | ~150 |
| Egg | 1 large | ~78 |
| Chicken breast, cooked | 2 oz | ~135 |
| White bread | 1 slice | ~75 |
| Cooked rice | 1 cup | ~205 |
| Slice of pizza (14") | 1 slice | ~285 |
| Hamburger | 1 sandwich | ~250 |
| Whole milk | 1 cup | ~146 |
| Beer | 1 can | ~154 |
Values are approximate and will vary by brand, preparation, and exact portion — use a nutrition label or food-tracking app for precise counts.
Calories Burned by Common Activities (1 Hour)
| Activity | 125 lb / 57 kg | 155 lb / 70 kg | 185 lb / 84 kg |
|---|---|---|---|
| Walking (3.5 mph) | 215 | 267 | 319 |
| Bicycling, moderate | 454 | 562 | 671 |
| Swimming, moderate | 397 | 492 | 587 |
| Tennis | 397 | 492 | 587 |
| Basketball | 340 | 422 | 503 |
| Running (9-min mile) | 624 | 773 | 923 |
Figures are approximate averages — actual calorie burn depends on intensity, fitness level, and individual metabolism.
Calorie-to-Kilojoule Converter
Calories and kilojoules both measure food energy — kilojoules are simply the metric unit, used on nutrition labels in many countries outside the US. The conversion is fixed: 1 calorie (kcal) = 4.1868 kilojoules (kJ). So a 2,000-calorie diet is equivalent to roughly 8,374 kJ. If a label shows kJ and you want calories, divide by 4.1868; to go the other way, multiply by 4.1868.
Frequently Asked Questions
What's the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the energy your body burns at complete rest. TDEE (Total Daily Energy Expenditure) takes BMR and multiplies it by an activity factor to estimate the calories you burn across a full day, including movement and exercise. The "calories to maintain weight" figure this calculator shows is your TDEE.
Which BMR formula is most accurate?
Mifflin-St Jeor is generally considered the most accurate for the general population today. The Katch-McArdle formula can be more precise for leaner or more athletic people, but only if you have an accurate body fat percentage to enter — a rough guess can make it less reliable than Mifflin-St Jeor.
How many calories should I eat to lose weight?
A common, sustainable approach is a deficit of around 500 calories a day below your maintenance level, which theoretically supports about 1 pound (≈0.45 kg) of weight loss per week. Cutting much more than about 1,000 calories a day below maintenance is generally discouraged, since faster loss increases the risk of muscle loss and metabolic slowdown.
Is calorie counting the best way to lose weight?
It's one of the most commonly used and reasonably effective approaches, since weight change ultimately comes down to calories consumed versus calories burned. That said, it isn't the only method, and factors like food quality, protein intake, and consistency also matter — the most sustainable approach is usually whichever method fits your lifestyle well enough that you'll actually stick with it.
How many calories do men and women need per day?
As a general guide, adult men typically need around 2,000–3,000 calories a day to maintain weight, and adult women around 1,600–2,400, depending heavily on age and activity level. Use the calculator above for a number personalized to your stats rather than relying on these broad ranges.
Does it matter what kind of calories I eat, or just the total?
For weight change specifically, total calories in versus calories out is what drives the scale. But food quality still matters for health, hunger, and sustainability — minimally processed foods rich in protein and fiber tend to be more filling and nutrient-dense per calorie than heavily processed or sugary options.
It's a way of varying your daily calorie intake — higher on some days, lower on others — while keeping the same total over a week. The goal is to add flexibility and potentially reduce the body's metabolic adaptation to a constant calorie level, compared with eating the exact same amount every single day.
Understanding BMI & Calories
BMI vs. Daily Calorie Needs
BMI tells you where you stand weight-wise. The calorie calculator tells you what to do about it — how many calories you need to maintain, lose, or gain weight in a healthy way. Used together, they give you both the diagnostic snapshot and the actionable daily target.
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