BMI Calculator
Calculate your body mass index from height and weight, see your category, and find the weight range that counts as healthy for your height.
BMI Calculator: with the default inputs, bmi is 23.7.
BMI itself ignores age, but the body-fat estimate below uses it, and under 20 the categories change entirely.
BMI is the same number for everyone. Sex is used only to interpret it: the body-fat estimate and the healthy body-fat range both differ.
- Category
- Healthy weight
- Healthy weight from
- 129 lb
- Healthy weight to
- 174 lb
- Change to reach healthy range
- 0 lb
- Estimated body fat
- 20.3%From BMI, age and sex (Deurenberg 1991). A population estimate, give or take about 4 points — it cannot see your build.
- Healthy body fat for your sex
- 14–24% (fitness to average)American Council on Exercise fitness-to-average band.
- Fat-free mass index
- —Lean mass ÷ height². Only shown when you enter a measured body fat. This is the figure that separates a muscular build from excess weight.
Assumptions
- BMI uses height and weight only. Age and sex are used for the body-fat estimate and its healthy range, never for the BMI itself.
- The body-fat estimate carries about 4 percentage points of error and, per the original paper, slightly overestimates in obese subjects.
- Fat-free mass index is shown only when you supply a measured body fat.
| BMI | Category | Weight(lb) |
|---|---|---|
| 18.5 | Healthy weight | 129 lb |
| 25 | Overweight | 174 lb |
| 30 | Obesity (class I) | 209 lb |
| 35 | Obesity (class II) | 244 lb |
| 40 | Obesity (class III) | 279 lb |
How this is worked out
The formula
BMI = weight (kg) ÷ height (m)² Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Height
- A number.in ft, in, cm, m · from 0.5 to 9 · defaults to 5.8333
- Weight
- A number.in lb, kg, st · from 1 to 1500 · defaults to 165
- Age
- BMI itself ignores age, but the body-fat estimate below uses it, and under 20 the categories change entirely.from 2 to 120 · whole numbers only · defaults to 35
- Sex
- BMI is the same number for everyone. Sex is used only to interpret it: the body-fat estimate and the healthy body-fat range both differ.Male · Female
- Measured body fat(under More options)
- Optional. If you have a real measurement — DEXA, calipers, the Navy tape method — entering it here computes your fat-free mass index, which is the number that tells muscle from fat. Leave at 0 to skip.a percentage · from 0 to 70 · defaults to 0
What you get back
- BMImain answer
- Category
- Healthy weight from
- Healthy weight to
- Change to reach healthy range
- Estimated body fat
- From BMI, age and sex (Deurenberg 1991). A population estimate, give or take about 4 points — it cannot see your build.
- Healthy body fat for your sex
- American Council on Exercise fitness-to-average band.
- Fat-free mass index
- Lean mass ÷ height². Only shown when you enter a measured body fat. This is the figure that separates a muscular build from excess weight.
What this assumes
- BMI uses height and weight only. Age and sex are used for the body-fat estimate and its healthy range, never for the BMI itself.
- The body-fat estimate carries about 4 percentage points of error and, per the original paper, slightly overestimates in obese subjects.
- Fat-free mass index is shown only when you supply a measured body fat.
About this calculator
Body mass index is a quick screen for whether your weight is in a range associated with good health. It's weight divided by height squared, and the WHO ranges are: under 18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30 and above obese.
What BMI can and can't tell you
BMI doesn't know how much of your weight is muscle, where you carry fat, or your bone density. Athletes routinely score "overweight" with very low body fat; older adults can have a "healthy" BMI while carrying too little muscle. Treat it as a starting point, then look at waist circumference, body-fat percentage, and how you feel and perform.
What the extra fields are for
BMI itself needs only height and weight. Age and sex do not enter the formula and never change the number. They are there because the number on its own tells you very little: the same BMI means a different body-fat percentage at 25 than at 65, and about ten percentage points' difference between men and women. The estimate shown alongside your BMI uses all three, and it is a population average with roughly four points of error either way — it cannot see your particular build.
If you know your actual body fat, enter it under More options. That switches the calculator to the fat-free mass index, lean mass over height squared, which is the figure that distinguishes a muscular build from excess weight. BMI cannot make that distinction at any level of sophistication, because the information is not in its inputs.
Ranges differ by population
Several health bodies use lower cutoffs for people of Asian descent (overweight from 23, obese from 27.5) because cardiometabolic risk rises at lower BMIs. Children and teens use age-and-sex percentile charts rather than fixed cutoffs.
Frequently asked questions
▸Why does the BMI calculator ask for sex if BMI is the same formula for everyone?
Because the number and its meaning are different things. BMI is weight over height squared and does not use sex at all — a man and a woman of the same height and weight have identical BMIs. What differs is what that BMI implies: at the same BMI, women carry roughly ten percentage points more body fat than men, and the healthy body-fat range differs accordingly. Sex is used here only for the body-fat estimate and that range, never for the BMI itself.
▸Does BMI account for muscle?
No, and it cannot. BMI knows only your height and your weight, so a heavily muscled athlete and someone carrying the same weight as fat get the same number. There is no version of BMI that fixes this, because the input simply is not there. What fixes it is measuring body fat — DEXA, calipers or the Navy tape method — and reading the fat-free mass index instead, which this calculator will work out if you enter a measured body fat.
▸What about body type — ectomorph, mesomorph, endomorph?
Somatotype has very little scientific support as a way to classify bodies, and it will not improve a BMI reading. If the question behind it is whether your weight is muscle or fat, the answer comes from measuring body composition, not from picking a body type.
▸What is a healthy BMI?
For adults, 18.5 to 24.9. The calculator translates that into a weight range for your exact height.
▸Is BMI accurate for athletes?
Not very. Muscle is denser than fat, so muscular people get high BMIs without excess fat. Body-fat percentage or waist-to-height ratio is a better check.
▸How do I calculate BMI by hand?
Divide your weight in kilograms by your height in meters squared. In pounds and inches, multiply weight by 703 and divide by height in inches squared.
▸Does BMI change with age?
The adult formula and cutoffs are the same from 20 onward. For ages 2–19, BMI is compared with growth-chart percentiles instead.
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