BMI calculator

Work out your body mass index from height and weight and see which category it falls into. Add your waist and you also get what BMI leaves out: whether the weight is fat or muscle.

Sex

Height (cm)

Weight (kg)

Waist circumference (cm, optional)

Measure standing, halfway between your lowest rib and the top of your hip bone, at the end of a relaxed breath out.

What are you after? (optional)

Fill in the fields to see your result instantly.

BMI categories for adults

Category	BMI
Underweight	< 18.5
Normal weight	18.5-24.9
Overweight	25.0-29.9
Obesity	30.0-34.9
Severe obesity	35.0-39.9
Morbid obesity	≥ 40

Limits: Finnish Current Care guideline on obesity 2025 and WHO (underweight). For people of Asian background the overweight limit is 23 and obesity 27.5. Children and teens use an age-adjusted BMI, not these limits.

Results are estimates intended for healthy adults. They do not replace advice from a doctor or dietitian.

The calculator is free and does not store the numbers you enter. If you have accepted analytics, we only record the BMI category and the goal you pick, so we know what people use the calculator for.

Same BMI, different story

Person	Body mass index (BMI)	Waist-to-height
Male, 180 cm, 92 kg, waist 84 cm	28.4 (Overweight)	0.47 (Healthy (under 0.5))
Male, 180 cm, 92 kg, waist 104 cm	28.4 (Overweight)	0.58 (Increased risk (0.5-0.59))
Female, 165 cm, 62 kg, waist 88 cm	22.8 (Normal weight)	0.53 (Increased risk (0.5-0.59))
Female, 165 cm, 58 kg, waist 72 cm	21.3 (Normal weight)	0.44 (Healthy (under 0.5))

The first two have exactly the same BMI, but only one has a waist that points to extra fat. The third is a normal weight, yet the waist-to-height ratio is raised.

From calculator to practice

BMI is one number. Your waist and your lifts tell the rest.

SisuLift tracks your weight, body measurements and training results in one app, so you can see whether a change is fat or muscle.

Weight trend as a weekly average, not daily swings
Waist and 13 other measurements as progress charts
Strength progress shows whether rising weight is muscle

Try SisuLift for free→

The free tier needs no card. Body measurements are part of Premium, which you can try for 14 days.

Your weight changes when you eat less or more than you burn. The calorie calculator shows how much that is for you.

How BMI is calculated

Body mass index is your weight in kilograms divided by your height in metres squared. For 180 cm and 80 kg: 80 / (1.8 × 1.8) = 24.7. The calculator rounds to one decimal and sets the category from the same number you see.

The formula goes back to the 1830s, when Belgian statistician Adolphe Quetelet was looking for the average person. It was built for studying populations, not for judging one person’s health, which is why it works best across large groups.

BMI categories and where the limits come from

The limits here follow the Finnish Current Care guideline on obesity (updated 2025), which matches WHO: normal weight 18.5-24.9, overweight 25-29.9, obesity 30-34.9, severe obesity 35-39.9 and morbid obesity 40 or more. Under 18.5 is underweight in the WHO classification.

The limits are the same for women and men. For people of Asian background health risks start lower, so the overweight limit is 23 and obesity 27.5. Children and teens have their own BMI that adjusts for age and sex.

Why BMI misleads people with a lot of muscle

BMI doesn’t know what your weight is made of. Muscle is denser than fat, so someone who has lifted for years can weigh as much as an overweight person of the same height without a gram of extra fat. At 180 cm and 92 kg, BMI calls you overweight (28.4) whether your waist is 84 or 104 cm.

The same error works the other way too. A person of normal weight can carry fat around the middle, and then BMI gives false comfort. Researchers call this normal weight central obesity.

That’s why this calculator asks for your waist. For anyone who trains, waist, body fat percentage and strength say more than BMI.

Your waist tells what BMI doesn’t

According to the Finnish Current Care guideline and THL, abdominal obesity starts above 100 cm for men and above 90 cm for women. Fat around the middle is linked to type 2 diabetes, high blood pressure and cardiovascular disease (NICE).

The UK’s NICE also recommends the waist-to-height ratio: keep your waist under half your height. Under 0.5 is healthy, 0.5-0.59 is increased risk and 0.6 or more is high risk. NICE says the ratio works for adults with a BMI under 35, including people with a lot of muscle.

Measure standing, halfway between your lowest rib and the top of your hip bone, at the end of a relaxed breath out. Keep the tape level and don’t pull it tight. Use the same spot and time of day so your measurements compare.

How to use your result

If both BMI and waist are in the healthy range, there’s no reason to worry about your weight. Training, sleep and food matter more than decimals.

If BMI is raised but your waist isn’t, the weight is most likely muscle, and body fat and strength are better measures. If both are raised, the calorie deficit calculator gives a realistic timeline and the ideal weight calculator shows what the formulas say about your height.

Sources

Frequently asked questions

What is BMI?

BMI, or body mass index, is your weight relative to your height. It’s the most common way to check whether an adult’s weight is in a healthy range. Normal weight is a BMI of 18.5-24.9.

How is BMI calculated?

Divide your weight in kilograms by your height in metres squared. 70 kg and 170 cm: 70 / (1.7 × 1.7) = 24.2. The calculator does the same and also shows your category and the normal weight range for your height.

What is a normal BMI?

18.5-24.9. For someone 175 cm tall, that means roughly 56.7-76.3 kg. The range is the same for women and men.

Why does BMI say I’m overweight when I lift?

BMI can’t tell muscle from fat. Someone who trains strength weighs more than an untrained person of the same height, even with less fat. Your waist-to-height ratio or body fat percentage shows which one your weight is.

What is a healthy waist size?

The Finnish Current Care limit for abdominal obesity is above 100 cm for men and above 90 cm for women. A simpler rule of thumb is NICE’s: keep your waist under half your height, so under 90 cm if you’re 180 cm.

Are BMI limits different for women and men?

No. BMI categories are the same for all adults. The difference is in waist size: the abdominal obesity limit is 90 cm for women and 100 cm for men.

Does BMI work for children and older adults?

Not for children and teens, who use a BMI that adjusts for age and sex. In older adults BMI is harder to read anyway, since muscle mass drops and height can shrink with age. Strength and waist size tell more there.

Can I track my weight and waist in SisuLift?

Yes. Your weight shows as a trend based on weekly averages, and your waist plus 13 other measurements show as progress charts in Premium. With your training in the same app, you can see from one place whether your strength goes up as your weight does.

The calculator gives you a number. SisuLift keeps it up to date.

Program, weights, nutrition and recovery in one app. The free tier needs no card, and the 14-day trial needs no card either.