Number One BMI Calculator
Choose metric or imperial, then enter your weight, height, and age. We calculate body mass index in your browser and place it on a visual scale — nothing is uploaded.
—
Healthy weightBackground
Body mass index is a short cut: weight in kilograms divided by height in metres squared. Adolphe Quetelet sketched it in the 1830s as a way to describe populations, not to judge a single body. Health services still use it because it is cheap, repeatable, and, at a group level, it tracks some risk.
For most adults it is a screening figure. It can flag that someone is much lighter or heavier than the average person of that height, and it is how many clinics, insurers, and public-health charts talk about underweight, healthy weight, overweight, and obesity. It is a starting point for a conversation, not the conversation itself.
BMI cannot see fat, muscle, bone, or where weight sits. A rugby player and someone with little muscle can share a number and have very different health. It also drifts with age, sex, ethnicity, pregnancy, oedema, and limb differences. Standard adult bands are a poor fit for children and teenagers — those results belong on growth charts. Older adults sometimes sit a little higher without extra risk. And a “healthy” BMI can still hide high blood pressure, low fitness, or a large waist.
Treat the number as a rough map. Waist size, how you feel day to day, blood markers, sleep, and what you can do with your body usually tell a fuller story. If the result worries you, take it to a qualified clinician rather than chasing the scale on your own.
Lifestyle
Lasting change is almost never a crash diet or a week of punishment in the gym. Bodies respond better to routines you can keep: enough food to fuel the day, movement you actually enjoy, sleep, and a bit of patience. The cards below are general tips, not a plan — and they are not a substitute for medical advice, especially if you have an eating disorder, are pregnant, or live with a long-term condition.
A modest energy gap works better than cutting whole food groups. Build plates around vegetables, protein, and fibre; drink water first; keep treats in the picture so the plan does not snap. Walk more weeks than you sprint. Strength work two or three times a week helps you keep muscle while the number on the scale eases down. Aim for roughly half a kilogram (about 1 lb) a week, not overnight.
Add nourishing extra rather than only extra sugar: nuts, dairy or fortified alternatives, olive oil, eggs, beans, and an additional snack. Pair that with resistance training so new weight is not only fat. Eat on a regular rhythm even when appetite is low, and give yourself time — sudden gain is as brittle as sudden loss. If food has become frightening or you are losing weight without trying, ask for clinical help.
Move most days in a way that raises your pulse and still leaves you able to talk. Sit less. Eat a mix of plants, protein, and foods you like, without moralising every plate. Sleep enough that the next day is possible. Go easy on alcohol and ultra-processed defaults. Progress is the week you can repeat, not the day you were perfect.
