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Free · No sign-up · Runs in your browser

Free BMI Calculator.

Work out your Body Mass Index instantly — enter your height and weight in metric or imperial and see your BMI, category and healthy weight range, right in your browser. Nothing here is ever uploaded.

Not uploaded — runs in your browser Metric & imperial support Healthy weight range included No subscription or account
Units
Height (cm)
Weight (kg)
BMI chart
Nothing here is ever uploaded — it’s all generated right in this browser tab, on your device. It never reaches a server, so we never see it, copy it or keep it.

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At a glance

BMI calculator: quick facts

Work out your Body Mass Index and healthy weight range in seconds.

Updated

Price
Free, no sign-up.
Units
Metric (kg and cm) or imperial (pounds, feet and inches).
Healthy range
18.5 to 24.9 for most adults, using the WHO thresholds the NHS uses.
You get
Your BMI, its category and the healthy weight range for your height.
Who it is for
Adults. Under-18s need an age-and-sex growth chart, such as the NHS children’s calculator.
Privacy
Worked out in your browser; nothing is sent anywhere.
How it works

How to work out your BMI

Enter your height and weight in metric or imperial units, and your BMI, its category and the healthy weight range for your height appear as you type.

  1. 01

    Choose your units

    Metric (cm and kg) or imperial (feet, inches and pounds) — whichever you find easier.

  2. 02

    Enter your height and weight

    Your BMI, category and healthy weight range update instantly as you type.

  3. 03

    Check the full chart

    See exactly where your result sits against every BMI category, from underweight to Obese Class III.

Tips

Tips for a more useful reading

BMI is a quick screening number, and a few habits make it more meaningful.

  • Measure carefullyWeigh yourself at the same time of day, ideally in the morning in light clothing, and measure your height without shoes. Being out by 2 cm on height can move your BMI by more than half a point.
  • Measure your waist as wellBMI doesn’t show where fat is stored. NHS advice is that, for most adults, a waist measurement of more than half your height can be a sign of increased health risk.
  • Watch the trend, not one readingWeight moves by a kilo or so from day to day with food and fluids. If you’re tracking your BMI, compare readings taken weeks apart rather than on back-to-back days.
  • Ask a professional about changesIf your result surprises you, or you’re planning to lose or gain weight, a GP or practice nurse can put it in context with your health and history.

Like every Altto tool, this runs on your device — nothing you add is uploaded. How Altto works

18.5–24.9

is the healthy BMI range for most adults, using the WHO thresholds the NHS uses.

FAQ

Frequently asked questions

What BMI is, how to read your result and where it falls short. Our BMI chart guide shows every category in full.

Source: the categories follow the NHS BMI calculator for adults. BMI is a general guide, not medical advice; talk to a GP about your own health.

What is BMI?
Body Mass Index (BMI) is a simple screening measure that divides your weight by the square of your height (kg ÷ m², or 703 × lb ÷ in²). It's used by the NHS and the World Health Organization as a quick, free way to flag whether someone's weight is likely to be in a healthy range for their height — not as a diagnosis on its own.
What's a healthy BMI range?
18.5–24.9 is classed as a healthy weight for most adults, using the same WHO thresholds the NHS uses. Below 18.5 is underweight, 25–29.9 is overweight, and 30 and above is obese, split further into Class I (30–34.9), Class II (35–39.9) and Class III (40+). The chart on this page shows every range at once.
Is BMI accurate for everyone?
No — BMI can't tell the difference between muscle and fat, so very muscular people (athletes, bodybuilders) are often classed as “overweight” or “obese” despite having low body fat. It's also not designed for use under 18, during pregnancy, or for older adults who've lost muscle mass, all of whom need a different way of assessing healthy weight. Treat a BMI result as a starting point for a conversation with a GP or pharmacist, not a verdict.
Does a healthy BMI differ by ethnicity?
The standard 18.5–24.9 range was developed mostly from data on white European populations. NHS guidance notes that people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background can face increased health risks at a lower BMI, and some NHS services use adjusted thresholds for these groups (around 23 for overweight and 27.5 for obese, instead of 25 and 30). This calculator uses the standard WHO scale; if this applies to you, it's worth mentioning to a GP or pharmacist alongside your result.
Can children use this calculator?
No. A child’s or teenager’s BMI has to be compared with others of the same age and sex, using growth charts, because their bodies change as they grow. The NHS has a separate BMI calculator that works this out for under-18s.
Why is my healthy weight shown as a range?
The healthy BMI band runs from 18.5 to 24.9, and for your height that band covers a range of weights. It’s a guide rather than a target, since people of the same height carry weight differently depending on muscle and build.
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