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BMI Calculator

Body mass index from your height and weight, in metric or imperial, with the healthy weight range for your height in the units you actually weigh yourself in. BMI is a rough screening tool rather than a verdict — the page is honest about what it cannot tell you.

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Ethnic background

The NHS uses a lower threshold — overweight from 23 rather than 25 — for these groups, because the risk of type 2 diabetes and heart disease begins at a lower BMI. It changes the answer, so it is worth setting.

Only used to check whether the adult categories apply. Under 18 they do not.

Loaded with an example. Type over any field.

Your BMI

25.5

Overweight

A BMI of 25.5 — 1.4 kg above the healthy range for your height

The bands

  • UnderweightUnder 18.5
  • Healthy weight18.5 – 25
  • Overweight — this is your band25 – 30
  • Obese30 – 40
  • Severely obese40 and over
Healthy weight range for your height
56.7–76.6 kg

The working

  1. Height: 175 cm = 1.75 m
  2. 1.75 × 1.75 = 3.0625 m²
  3. BMI: 78 kg ÷ 3.0625 m² = 25.5
  4. Healthy range for this height: 56.7–76.6 kg

BMI is a rough screening tool, not a diagnosis. It cannot tell muscle from fat and says nothing about where weight is carried, which is what actually matters for health. Athletes often read as overweight; someone in the healthy band can still carry too much around the middle. If you are worried about your weight, speak to a GP or a pharmacist.

Check this before you rely on it. A free everyday calculator, provided as a guide — not tax, accounting, financial or legal advice. The working is shown above so you can verify it against your own figures. See our terms of use.

How it works

STEP 1

Enter height and weight

Centimetres and kilograms, or feet, inches, stone and pounds. The tabs switch between them and the answer is identical either way — only the units on screen change.

STEP 2

Set your background if it applies

Under Refine. The NHS uses a lower overweight threshold — 23 rather than 25 — for people of Black African, African-Caribbean or South Asian background. It moves the bands, so it is worth setting.

STEP 3

Read the range, not just the number

A BMI on its own is hard to act on. The healthy weight range for your height, in stone or kilograms, tells you what the number actually means for you.

What this doesn't cover

Knowing where a calculator stops is what makes the rest of it trustworthy.

  • Muscle versus fatBMI is weight over height squared and nothing else. It cannot tell dense muscle from body fat, so a well-trained athlete frequently reads as overweight or obese while being nothing of the kind.
  • Where the weight sitsWeight carried around the middle carries more health risk than the same weight elsewhere, and BMI is blind to it. Waist measurement is the usual companion check — the NHS suggests keeping your waist under half your height.
  • Children and teenagersUnder 18, BMI is read against age-and-sex growth charts rather than fixed numbers, so the adult categories do not apply. Enter an age under 18 and the calculator withholds the category rather than showing one it cannot stand behind.
  • Pregnancy, illness and older ageBMI is not meaningful during pregnancy, and it becomes a weaker guide in older adults, where a slightly higher reading is often not a problem. Any of these is a reason to ask a professional rather than a website.
The guideHow to calculate BMI — and what the number can’t tell youBMI is your weight in kilograms divided by your height in metres squared. For most adults 18.5 to 24.9 is the healthy range — though the NHS uses lower thresholds for some ethnic backgrounds.Read it

Common questions

How is BMI calculated?

Weight in kilograms divided by height in metres squared. Someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial it is pounds ÷ inches², multiplied by 703 — this calculator converts your figures and shows the arithmetic either way.

What is a healthy BMI?

18.5 to 24.9 is the healthy range for most adults. Below 18.5 is underweight, 25 to 29.9 overweight, and 30 or above obese. If your background is Black African, African-Caribbean or South Asian, the NHS uses lower cut-offs — 23 for overweight and 27.5 for obese.

Why are the thresholds lower for some ethnic groups?

Because the health risk starts sooner. At the same BMI, people of South Asian, Black African and African-Caribbean background have a higher risk of type 2 diabetes and heart disease, so the NHS lowered the overweight threshold to 23 and the obese threshold to 27.5 for those groups. A calculator using only 25 and 30 would tell a lot of people they are fine when their GP would not.

Is BMI accurate?

It is accurate arithmetic and a crude health measure — those are different things. It works reasonably well across a population and poorly for individuals at the edges. It cannot distinguish muscle from fat, ignores where weight is carried, and does not know your age, fitness or medical history. Treat it as one number among several, not a verdict.

Does BMI work for athletes?

Often not. Muscle is denser than fat, so a rugby player or a serious weightlifter can be in excellent health and still show a BMI of 30. If you carry a lot of muscle, BMI will overstate your risk and a body-fat measurement or a waist reading is more useful.

What about children?

The adult bands do not apply. A child’s BMI is compared against growth charts for their exact age and sex, because healthy BMI changes throughout childhood. Enter an age under 18 here and the calculator shows the number but withholds the category. For a child, use the NHS healthy weight calculator or ask a GP or school nurse.

My BMI is in the overweight band — what should I do?

Nothing this website tells you. BMI is a screening number that suggests whether a conversation is worth having, not a diagnosis and not a plan. A GP or a pharmacist can look at your waist, blood pressure, family history and everything else BMI cannot see. That is the right next step, and it is free.

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