The BMI Calculator is a free tool that helps you calculate bmi using the formula BMI = weight(kg) / height(m)^2. Enter your values above and press Calculate to get bmi instantly, with a full step-by-step breakdown.
What is the BMI Calculator?
The bmi calculator is a free online tool that helps you calculate bmi quickly and accurately. It applies the standard formula BMI = weight(kg) / height(m)^2 to the values you enter and, when you press Calculate, displays the result together with a clear, step-by-step explanation of how the answer was reached.
Also known as: bmi, bmi calculator women, bmi formula, bmi calculator male, bmi chart, body mass index.
How to use the BMI Calculator
- Enter your weight in kilograms.
- Enter your height in centimetres.
- Read your BMI and category.
Formula used
The bmi calculator is based on this formula:
BMI = weight(kg) / height(m)^2Each term in the formula corresponds to one of the inputs explained below. The calculator performs the arithmetic for you and shows every step so you can check the working by hand if you wish.
Worked example
Suppose you enter 70 kg, 170 cm. The calculator works as follows:
| Inputs | 70 kg, 170 cm |
|---|---|
| Working | 70 / 1.70^2 |
| Result | BMI = 24.2 (Normal) |
Step-by-step calculation
- Apply the formula:
BMI = weight(kg) / height(m)^2 - Substitute your values: 70 / 1.70^2
- Read the result: BMI = 24.2 (Normal)
BMI categories (WHO, adults)
| Classification | BMI range (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese Class I | 30 – 34.9 |
| Obese Class II | 35 – 39.9 |
| Obese Class III | 40 and above |
Inputs explained
- Weight (kg) — the weight used in the calculation.
- Height (cm) — the height used in the calculation.
Understanding your result
- BMI — the calculated bmi.
Benefits and practical uses
The bmi calculator saves time and removes the risk of manual errors when you need to calculate bmi. It is useful for students, professionals and anyone who wants a fast, dependable answer. Results update the moment you press Calculate, work on any device, and can be copied or shared in a single click — and because the maths runs in your browser, your figures stay completely private.
Tips for an accurate result
- Keep all related inputs in the same units.
- Use the worked example above to confirm you are entering values in the right places.
- Review the assumptions below so the result fits your situation.
- Press Reset to clear everything and try a different scenario.
Common mistakes to avoid
- Entering values in the wrong unit (mismatched units give wrong answers).
- Leaving a required field empty — the calculator will ask you to fill it in.
- Treating the result as a diagnosis instead of a general guide.
Assumptions and limitations
- Adult BMI categories (WHO).
- Not valid for children, pregnancy or athletes.
Frequently asked questions
What is a healthy BMI?
For adults, 18.5-24.9 is considered normal. Below 18.5 is underweight and 25+ is overweight.
Is BMI accurate for everyone?
BMI does not distinguish muscle from fat, so it can misclassify athletes and the elderly. Use it as a general screen.
How do I use the BMI Calculator?
Enter your values in the fields, then press the Calculate button to see the result. Use Reset to clear the form and start again. Nothing is calculated until you click Calculate.
What formula does the BMI Calculator use?
It uses the standard formula: BMI = weight(kg) / height(m)^2. The full step-by-step working is shown with every result so you can verify it.
What information do I need to use the bmi calculator?
You need: weight, height. Sensible example values are pre-filled so you can see how it works.
Is the BMI Calculator free to use?
Yes. Every DigiToolkit calculator is completely free, with no sign-up, no login and no usage limits.
Does the BMI Calculator work on mobile phones?
Yes. The calculator is mobile-first and works on phones, tablets and computers in any modern browser.
Do I need to install an app?
No. The bmi calculator runs directly in your web browser — there is nothing to download or install.
Is my data private when I use this calculator?
Yes. All calculations run inside your browser. The numbers you enter are never uploaded to a server or shared with anyone.
How accurate is the BMI Calculator?
It uses the generally accepted formula for bmi and computes to several decimal places. Results are accurate for the assumptions listed on this page.
Can I copy or share my result?
Yes. After calculating, use the Copy button to copy the result, or Share to copy the page link.
Why is nothing showing until I press Calculate?
By design, the calculator only computes when you press Calculate, so you can finish entering all your values first. Press Reset any time to clear everything.