BMI Calculator (Free — Metric & Imperial)
Use this free BMI calculator to instantly find your Body Mass Index. Works in both metric (kg and cm) and imperial (lbs, feet and inches). See your BMI category, healthy weight range for your height, and personalised guidance.
BMI Calculator
<18.5 Healthy
18.5–24.9 Overweight
25–29.9 Obese
30+
📊 BMI Categories
How to Use the BMI Calculator
Choose metric or imperial units, enter your weight and height, then click Calculate. Your BMI, category, healthy weight range and how much to lose or gain will show instantly.
How Is BMI Calculated?
BMI is calculated by dividing your weight in kilograms by your height in metres squared.
Metric formula: BMI = Weight (kg) ÷ Height² (m²)
Imperial formula: BMI = 703 × Weight (lbs) ÷ Height² (inches²)
For example someone who weighs 70kg and is 1.75m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9 — which is in the healthy range.
BMI Categories
- Underweight — below 18.5
- Healthy Weight — 18.5 to 24.9
- Overweight — 25 to 29.9
- Obese — 30 to 34.9
- Severely Obese — 35 and above
Limitations of BMI
BMI is a useful screening tool but doesn’t directly measure body fat. Athletes with high muscle mass may have a high BMI despite being very lean. BMI also doesn’t account for age, gender differences in body composition, or where fat is distributed in the body. Use BMI as a general guide alongside other health measures.
FAQs
What is a healthy BMI?
A BMI between 18.5 and 24.9 is considered healthy for most adults. However healthy BMI ranges can vary slightly by age and ethnicity.
What is the difference between BMI and body fat percentage?
BMI is a simple calculation based on height and weight. Body fat percentage measures the actual proportion of fat in your body and is more accurate but requires specialist equipment.
Does BMI work for children?
This calculator is designed for adults. Children and teenagers should use age and gender specific BMI charts as healthy ranges differ during growth stages.
Can I use this in pounds and feet?
Yes — simply toggle to Imperial at the top of the calculator and enter your weight in pounds and height in feet and inches.
Is BMI accurate?
BMI is a widely used screening tool but has limitations. For a fuller picture of your health use it alongside other measures like waist circumference and body fat percentage.
Is this calculator free?
Yes, completely free with no sign-up needed.