Know your numbers.
Enter your height, weight and age and this tool works out your BMI, waist-to-height ratio and daily energy needs from the Mifflin-St Jeor equation, shown in kcal and kJ. Every figure sits on a scale next to the range it falls in, explained in plain language rather than as a verdict.
Your numbers, read together.
Set your height, weight, age, sex and activity level. Add your waist if you have it to hand, for the waist-to-height ratio. Nothing you enter leaves this page.
Height (cm)
Measured around the belly button, standing, after breathing out.
Sex
Used only in the Mifflin-St Jeor energy formula.
The WHO classes an adult BMI under 18.5 as underweight, 18.5 to 24.9 as a normal weight range, 25 to 29.9 as overweight and 30 or higher as obese.
A ratio of 0.50 or higher, a waist that reaches half your height, is the line most studies use to flag a higher average cardiometabolic risk.
BMI does not tell muscle from fat and is not used for children, pregnant women or athletes. Waist-to-height ratio and BMR come from population averages, not a measurement of your own body.
How it works.
- Set your height, weight and age, choose your sex for the energy formula and pick an activity level; add your waist if you have it to hand.
- Read your BMI on the WHO scale, your waist-to-height ratio if you entered a waist, and your resting and daily energy in kcal and kJ.
- Switch between metric and imperial at any point, then copy the summary if you want to keep it or share it with a trainer or clinician.
What each number measures
Body mass index divides your weight in kilograms by the square of your height in metres. The World Health Organization classes an adult BMI under 18.5 kg/m2 as underweight, 18.5 to 24.9 kg/m2 as a normal weight range, 25 to 29.9 kg/m2 as overweight and 30 kg/m2 or higher as obese. Waist-to-height ratio divides your waist by your height in the same unit; 0.50 is the line most studies use, because a waist that reaches half your height marks fat carried centrally rather than on the hips or thighs. Resting energy, or BMR, follows the Mifflin-St Jeor equation: 10 times your weight in kilograms plus 6.25 times your height in centimetres minus 5 times your age in years, plus 5 for men or minus 161 for women. Multiplying BMR by an activity factor from 1.2 for a sedentary day to 1.9 for very hard training gives TDEE, your estimated total energy for that day, shown in kilocalories and kilojoules, where 1 kcal equals 4.184 kJ.
Where the numbers come from
The WHO BMI bands date from a 1995 expert consultation and remain the reference most doctors still cite, even though BMI cannot tell muscle from fat. Waist-to-height ratio has been tested against BMI and waist circumference alone in dozens of studies; pooled analyses covering hundreds of thousands of adults found it predicted diabetes, heart disease and early death at least as well as BMI, and often better, using the same 0.50 cut-off in both men and women. The Mifflin-St Jeor equation, published in 1990 from measurements of over 400 adults, has outperformed the older Harris-Benedict formula from 1919 in repeated validation studies, particularly in adults who carry more weight, which is why dietitians favour it today for resting energy.
What this tool is not
None of these numbers diagnose anything. BMI treats a well-muscled frame the same as a fat-heavy one at the same weight and height, so it is not used for children, for pregnant or breastfeeding women, or for athletes with a lot of muscle mass: the guide on connective tissue and the one on where vitality shows first both look past a single ratio. BMR and TDEE are population averages built from group data, not a measurement of your own metabolism, and they say nothing about strength, fitness or recovery, ground the sports massage guide covers instead. Treat the figures here as a starting point for a conversation, not a target to chase, and a large or sudden weight change as a reason to see a doctor rather than to recalculate.
Frequently asked.
Why do I need to give my sex for the energy numbers?
The Mifflin-St Jeor equation adds 5 kcal for men and subtracts 161 kcal for women to account for the average difference in muscle mass at the same height and weight. It is a population average, not a measurement of your own body composition.
What does the waist-to-height ratio tell me that BMI does not?
BMI cannot see where fat sits. Several meta-analyses report that a waist-to-height ratio at or above 0.50 tracks cardiometabolic risk at least as closely as BMI, because it flags fat carried around the waist specifically.
Is BMR the number of calories I burn in a day?
No, BMR is the energy your body uses at complete rest, roughly what you would burn lying still for 24 hours. TDEE adds the activity factor you chose and is the closer estimate for a full day.
Why is this tool not meant for children, pregnancy or athletes?
The WHO adult BMI bands and the Mifflin-St Jeor equation were built from and checked against non-pregnant adults with average muscle mass. Children need growth charts, pregnancy changes weight for reasons unrelated to fat, and athletes can carry enough muscle to read as overweight on BMI alone.
Does switching to imperial change the result?
No. Height, weight and waist convert between centimetres, kilograms and their imperial equivalents behind the scenes, so the same body gives the same BMI, ratio and energy figures in either unit.
Is anything I enter saved or sent anywhere?
Your figures stay in your browser only, saved locally so the tool remembers them on your next visit. Nothing is sent to a server.
Guides behind this tool
Skin and Cosmetics
Cellulite: the connective tissue question
Skin and Cosmetics
Radiance: what comes before cosmetics
Massage
Sports massage: timing determines the techniqueMore tools
Body Metrics estimates BMI, waist-to-height ratio and energy needs from standard population formulas; it does not diagnose a health condition and does not replace an assessment by a doctor or registered dietitian. This page is for general information and does not replace medical or professional cosmetic advice.