Calculating your BMI is straightforward once you know the BMI formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the BMI Calculator.
What is BMI?
The BMI calculation tells you your BMI from a few simple inputs. The figure you are solving for here is the BMI.
The BMI formula
This calculation combines several inputs through a multi-step method rather than a single one-line formula. Enter the values below and the calculator resolves each step in order. The inputs it needs are:
- Weight — a value measured in kg. Example: 70 kg.
- Height — a value measured in cm. Example: 170 cm.
How to calculate it step by step
- Write down the weight (for example, 70 kg).
- Write down the height (for example, 170 cm).
- Apply the formula above to get your BMI.
- Double-check the result with the BMI Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Weight | 70 kg |
| Height | 170 cm |
| Your BMI | 24.2 |
| Category (0=under,1=normal,2=over,3=obese) | 1 |
| Healthy weight (min) | 53.5 kg |
| Healthy weight (max) | 72.0 kg |
With weight of 70 kg and height of 170 cm, the BMI works out to 24.2.
Example 2
With weight of 140 kg and height of 170 cm, the BMI works out to 48.4.
| Result | Value |
|---|---|
| Your BMI | 48.4 |
| Category (0=under,1=normal,2=over,3=obese) | 3 |
| Healthy weight (min) | 53.5 kg |
| Healthy weight (max) | 72.0 kg |
Example 3
With weight of 35 kg and height of 170 cm, the BMI works out to 12.1.
| Result | Value |
|---|---|
| Your BMI | 12.1 |
| Category (0=under,1=normal,2=over,3=obese) | 0 |
| Healthy weight (min) | 53.5 kg |
| Healthy weight (max) | 72.0 kg |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
- These figures are general estimates, not medical advice — check with a qualified professional before acting on them.
Prefer not to do the maths by hand? — the BMI Calculator does it instantly, for free, with the formula and a worked example built in.
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