Free online calculator
BMI calculator
Check BMI and estimated BMR.
BMI and BMR calculator
Enter height, weight, sex, and age to see your BMI category and estimated BMR.
How to use this calculator
- 1
Choose your unit system
Toggle between metric (kg / cm) and imperial (lb / ft + in).
- 2
Enter height and weight
Type your current height and weight in the fields provided.
- 3
Set sex and age
Select male or female and enter your age in years — both are needed for the BMR calculation.
- 4
Read your results
Check your BMI score, weight category badge, and estimated BMR.
Formula
BMI: weight (kg) ÷ height (m)²
BMR — male: 10w + 6.25h − 5a + 5
BMR — female: 10w + 6.25h − 5a − 161
where w = weight in kg, h = height in cm, a = age in years.
Worked example
Male, 70 kg, 170 cm, age 30:
BMI = 70 ÷ 1.70² = 24.22 → Normal weight.
BMR = 10×70 + 6.25×170 − 5×30 + 5 = 700 + 1062.5 − 150 + 5 = 1617 kcal/day.
FAQ
Is BMI accurate for athletes? +
BMI does not distinguish between fat and muscle mass. Athletes with high muscle mass may have a high BMI despite low body fat. It is best used as a population screening tool rather than an individual diagnostic.
What's the difference between BMI and BMR? +
BMI (body mass index) is a height-to-weight ratio that indicates a weight category. BMR (basal metabolic rate) estimates the calories your body burns at complete rest — useful as a starting point for setting daily calorie targets.
What's a healthy BMI range? +
For adults, a BMI of 18.5 to 24.9 is considered a healthy weight by the World Health Organisation. Below 18.5 is underweight; 25–29.9 is overweight; 30 or above is obese.
Do children use the same BMI scale? +
No. Child and teen BMI is interpreted using age- and sex-specific percentile charts, not the fixed adult thresholds. This calculator is designed for adults aged 18 and over.
What is the Mifflin-St Jeor formula? +
Mifflin-St Jeor is a widely used equation that estimates resting calorie needs from weight, height, age, and sex. For men: 10w + 6.25h − 5a + 5. For women: 10w + 6.25h − 5a − 161 (w in kg, h in cm, a in years).
About this calculator
This BMI calculator computes your body mass index and weight category using the standard WHO thresholds, and also estimates your basal metabolic rate — the calories your body burns at rest — via the Mifflin-St Jeor formula. Results apply to adults only; child BMI uses age- and sex-specific growth charts that are outside the scope of this tool.
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