BMI Calculator

Body Mass Index is the quick screening number doctors, insurers and fitness programmes use to flag whether a person’s weight is in a healthy range for their height. Our free BMI calculator does the maths instantly in metric (kilograms and centimetres) or imperial (pounds, feet and inches) units. Alongside your BMI value and its standard category, it shows the healthy weight range for your height, so you get context rather than a bare number. Remember that BMI is a general guide, not a diagnosis; muscular builds and other factors can shift the picture.

Quick Answer: Enter your height and weight in metric or imperial units. The calculator shows your BMI, its category (underweight, healthy, overweight or obese) and the healthy weight range for your height.

Free Online Tool

Your Body Mass Index and the healthy range for your height.

Unit system

Weight (kg)

Height (cm)

Table of Contents

How to Use the BMI Calculator

Choose your unit system: metric (kg and cm) or imperial (lb, feet and inches).
Enter your height and weight honestly; guessing undermines the point of the check.
Read your BMI value and the category it falls into.
Compare your weight with the healthy range shown for your height to see how far you are from it, in either direction.
Recheck monthly rather than daily if you are tracking change; healthy weight moves slowly.

Key Features

Dual unit systems with feet-and-inches support for imperial users.
Instant category classification using the standard World Health Organization ranges.
Personalised healthy weight range calculated for your exact height.
Clean, judgement-free presentation focused on information, not appearance.
Runs privately in your browser; health data is never uploaded or stored.

Best Practices and Tips

Measure height without shoes and weight in light clothing, ideally at the same time of day, for consistent comparisons.
Treat BMI as a starting signal; waist measurement and how you feel and perform add important context.
Athletes and very muscular people often score ‘overweight’ because muscle is dense; a body-composition check is fairer for them.
Children and teenagers need age-and-sex percentile charts, not adult BMI categories; do not apply this scale to them.
Pair any BMI goal with a waist measurement goal; the two together track health change far more honestly than weight alone, especially if you are also building muscle.

Common Mistakes to Avoid

Panicking over a single reading near a boundary; a kilogram of water retention can move the number without meaning anything.
Comparing your BMI with a friend’s without considering build, age and muscle mass differences.
Using BMI as the only health target; fitness, blood pressure, sleep and diet quality all matter alongside it.

Frequently Asked Questions

What is a healthy BMI range?

For most adults, 18.5 to 24.9 is classified as healthy. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or above is obese. These are the standard WHO categories used worldwide.

How is BMI calculated?

BMI equals weight in kilograms divided by height in metres squared. A person of 70 kg and 1.75 m has a BMI of 70 ÷ (1.75 × 1.75), which is about 22.9. This calculator performs the same formula in either unit system.

Why might BMI be misleading for me?

BMI cannot distinguish muscle from fat or see where fat is carried. Bodybuilders, pregnant women, the elderly and some ethnic groups get skewed readings, which is why clinicians combine BMI with other checks.

Does BMI apply to children?

Not with adult categories. Children are assessed with BMI percentiles that account for age and sex, because healthy body composition changes rapidly while growing. Use a paediatric chart or your doctor for under-18s.

How often should I check my BMI?

Monthly is plenty when you are working on gradual change. Daily weight fluctuates with water and food, and chasing those swings through BMI only adds noise and stress.

I am pregnant or breastfeeding. Does BMI apply?

No. Weight during pregnancy and the months after birth follows its own guidance, and standard BMI categories should not be used to judge it. Your clinician tracks healthy ranges for pregnancy specifically, which replace the general adult scale entirely.