To calculate your BMI, choose Metric or Imperial, enter your height and weight, and select Calculate BMI. BMI is your weight in kilograms divided by your height in meters squared. A result from 18.5 to under 25 is in the healthy range for adults; 25 to under 30 is overweight, and 30 or more is obesity.
How to use the BMI calculator
- Pick your units. Select Metric for cm and kg, or Imperial for feet, inches and pounds.
- Enter your details. Fill in Sex, Age, height and weight. Age and sex don't change adult BMI, but they're used for BMR, TDEE and the body fat estimate.
- Set activity and goal (optional). Choose an Activity Level, a Goal (Maintain, Lose or Gain Weight) and a Goal Speed of 250, 500 or 750 kcal a day. Add your waist measurement to get a waist-to-height ratio, and your neck (plus hip for women) for a body fat estimate.
- Calculate. Select Calculate BMI. Your BMI, category, healthy weight range, BMR, TDEE and goal calories appear below, and the result is saved to your browser history if that option is ticked.
How is BMI calculated?
BMI (body mass index) compares weight to height:
- Metric:
BMI = weight (kg) / height (m)^2 - Imperial:
BMI = 703 x weight (lb) / height (in)^2
Worked example with the calculator's default values: 70 kg and 175 cm. Height in meters is 1.75, and 1.75 x 1.75 = 3.0625. Then 70 / 3.0625 = 22.9, which is in the healthy range. In Imperial mode the same person is 5 ft 9 in (69 in) and 154.3 lb: 703 x 154.3 / 4,761 = 22.8. (rounding explains the small gap).
BMI chart: adult categories
The calculator uses the CDC's adult BMI categories for people aged 20 and over. The World Health Organization uses the same cut-off points for adults.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to under 25 | Healthy weight |
| 25 to under 30 | Overweight |
| 30 to under 35 | Obesity, class 1 |
| 35 to under 40 | Obesity, class 2 |
| 40 or higher | Obesity, class 3 (severe) |
The tool reports the four main groups (Underweight, Healthy Weight, Overweight, Obesity). It doesn't split obesity into classes, so use the table above if you need that detail.
What is a healthy weight for my height?
The healthy range is the weight that gives a BMI of 18.5 to 24.9 at your height, the same range the calculator shows under Healthy Weight Range, in kilograms or, in Imperial mode, pounds.
| Height | Healthy weight | Height | Healthy weight |
|---|---|---|---|
| 150 cm | 41.6-56.0 kg | 5 ft 0 in | 95-128 lb |
| 160 cm | 47.4-63.7 kg | 5 ft 4 in | 108-145 lb |
| 170 cm | 53.5-72.0 kg | 5 ft 8 in | 122-164 lb |
| 180 cm | 59.9-80.7 kg | 6 ft 0 in | 136-184 lb |
| 190 cm | 66.8-89.9 kg | 6 ft 4 in | 152-205 lb |
The separate Ideal Weight figure is an average of the Robinson, Miller and Devine formulas, plus or minus 2 kg, shifted 1.5 kg down or up for a small or large Frame Size.
BMR, TDEE and calorie targets
BMR (basal metabolic rate) is an estimate of the calories you burn at rest. The calculator uses the Mifflin-St Jeor equation:
- Men:
10 x kg + 6.25 x cm - 5 x age + 5 - Women:
10 x kg + 6.25 x cm - 5 x age - 161
For a 25-year-old man at 70 kg and 175 cm: 700 + 1,093.75 - 125 + 5 = 1,674 kcal a day. TDEE multiplies BMR by your Activity Level: 1.2 (Sedentary), 1.375 (Lightly Active, the default), 1.55, 1.725 or 1.9 (Extra Active). Here that's 1,674 x 1.375 = about 2,301 kcal. Goal calories add or subtract your Goal Speed, and a weight-loss target never goes below 1,200 kcal.
With a waist size entered, the waist-to-height ratio is waist divided by height. Below 0.5 is labeled Healthy, in line with the UK NICE advice to keep your waist under half your height.
For body fat, enter your waist and neck (and hip, for women) and the calculator uses the US Navy tape-measure formula, with all sizes in cm:
- Men:
495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450 - Women:
495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.221 x log10(height)) - 450
The Sample Male (178 cm, waist 82 cm, neck 39 cm) comes out at about 13.2%. Measure the waist at the navel and the neck just below the larynx. Without those measurements, the figure falls back to the Deurenberg formula (1.2 x BMI + 0.23 x age - 10.8 for men - 5.4), a rougher estimate from BMI, age and sex only. The result says which method it used.
When BMI can mislead: athletes, older adults and children
BMI is a screening number. It doesn't measure body fat or tell muscle from fat.
- Athletes and muscular people can score as overweight with little body fat.
- Older adults often lose muscle, so a normal BMI can hide extra body fat.
- Children and teens (ages 2 to 19) need BMI-for-age percentiles. The CDC classes below the 5th percentile as underweight, the 5th to under 85th as healthy, the 85th to under 95th as overweight and the 95th or above as obesity.
This tool accepts ages from 5, but it isn't a child BMI calculator. For anyone under 20 it shows the BMI number with a clear note that adult categories don't apply, leaves out the category, healthy weight range, ideal weight, goal calories and body fat, and links to the CDC's Child and Teen BMI Calculator, which gives the BMI-for-age percentile. You can also ask a pediatrician. This calculator gives estimates, not medical advice. Talk to a doctor before acting on any result.
Frequently asked questions
BMI calculator for men: is it different from women?
No. Adult BMI uses the same formula and the same categories for men and women. Sex only changes the BMR, calorie and body fat estimates in this tool, and the body fat formula asks women for a hip measurement too.
Why does this BMI calculator in kg ask for my age?
Age doesn't change adult BMI: 70 kg at 175 cm is 22.9 at 25 or at 65. The calculator uses age for BMR, calorie and body fat estimates. If you only know a birth date, the age calculator gives your exact age.
Can I use this as a child BMI calculator?
No. Adult categories aren't valid for children, so for ages under 20 the calculator shows only the BMI number and points you to the CDC's Child and Teen BMI Calculator. Kids and teens aged 2 to 19 are assessed with sex-specific BMI-for-age percentiles from the CDC growth charts.
Where are my saved BMI results stored?
In your browser's local storage on this device. The last 25 results are kept, you can download them with Export JSON, and Clear History deletes them. Nothing is sent to a server.
Can I enter my height in feet and inches?
Yes. Select Imperial, then enter Height (ft), Extra Inches and Weight (lb). For other conversions, the unit converter handles cm, inches, kg and pounds.