Boring Tools

BMI Calculator

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Calculate Body Mass Index from height and weight.

Work out your Body Mass Index (BMI) from your height and weight, in metric or imperial units, and see which standard adult category it falls into. BMI is a rough screening number, not a diagnosis.

How it works

BMI = weight in kilograms ÷ (height in metres)². If you use imperial units, feet and inches are converted to centimetres (1 inch = 2.54 cm) and pounds to kilograms (1 lb = 0.45359237 kg) first. The result is shown to one decimal place.

The category uses the standard adult bands: under 18.5 is Underweight, 18.5 to under 25 is Normal weight, 25 to under 30 is Overweight, and 30 or more is Obese.

How to use it

  1. Choose Metric or Imperial with the toggle.
  2. Enter your height (in centimetres, or in feet and inches) and your weight (in kilograms or pounds).
  3. Read your BMI and its category in the result panel.
  4. Click Copy to copy the result as text.

Options & controls

Units

Metric / Imperial toggle
Switches between centimetres and kilograms, and feet/inches and pounds. This is a site-wide setting shared with the other calculators that use it, so your choice carries over to them, and it is remembered in this browser.

Inputs

Height (metric)
One box, in centimetres. Must be greater than 0. Default: 170.
Height (imperial)
Two boxes, Feet and Inches. Inches may be a decimal. The total must be greater than 0. Default: 5 ft 7 in.
Weight
One box, in kilograms (metric) or pounds (imperial). Must be greater than 0. Default: 65 kg or 143 lb.
Reset
In the title row. Restores the sample values for both unit systems (the chosen unit system itself is kept).

Reading the results

Result

BMI value
The number, to one decimal place.
Category
Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9) or Obese (30 and above).
Copy
Copies the result as text, e.g. “BMI: 22.5 (Normal weight)”.
Placeholder
“Enter your height and weight” shows until both are valid positive numbers.

Tips & guidelines

  • Each unit system keeps its own set of boxes. Switching from metric to imperial does not convert what you typed; enter your figures again in the new units.
  • Measure height without shoes and weight at a consistent time of day for comparable results over time.
  • Treat the category as a starting point for a conversation with a health professional, not as a verdict.

Limits

  • The bands are for adults. They do not apply to children and teenagers (whose BMI is judged against age- and sex-specific charts), and BMI can be misleading during pregnancy.
  • BMI cannot tell muscle from fat, so people who are very muscular may be classed as overweight, and it does not show where body fat is carried. Some health bodies use different cut-offs for some ethnic groups.
  • This tool does not give a healthy weight range or health advice, and nothing here is medical advice.

Saved in your browser

Your height and weight are not saved. Only the Metric / Imperial choice is remembered in this browser, and it is shared with other tools that use it.

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