Free tool · Health
BMI Calculator
Enter your height and weight to see your body mass index, its WHO category and the healthy weight range for your height.
BMI for 70 kg and 175 cm?
22.9
Your BMI falls in the WHO Normal range. This is a screening category, not a judgement of your health.
- Healthy weight range for your height
- 56.7 – 76.3 kg
- BMI Prime (BMI ÷ 25)
- 0.91
- Height-corrected BMI (Trefethen)
- 22.5
- Waist-to-height ratio
- —
How to use this BMI calculator
- Choose Metric or Imperial — kilograms and centimetres, or pounds, feet and inches.
- Enter your weight and height. The result updates as you type.
- Optionally add your waist measurement to see your waist-to-height ratio.
- Read your BMI, your WHO category, the healthy weight range for your height, BMI Prime, and the height-corrected BMI.
Your BMI is calculated from your height and weight. The category shown uses WHO adult BMI classifications. BMI is a screening measurement, not a diagnosis.
The formula, in plain words
Body Mass Index (BMI) is a calculation that compares weight with height. It is a general screening tool, not a direct measure of body fat.
BMI = weight (kg) ÷ height (m)²
Convert your height from centimetres to metres, multiply the height by itself, then divide your weight by the result. In imperial units the same formula carries a conversion factor of 703:
BMI = 703 × weight (lb) ÷ height (in)²
Worked example — 70 kg and 175 cm
- Convert height to metres: 175 ÷ 100 = 1.75 m.
- Square the height: 1.75 × 1.75 = 3.0625.
- Divide weight by squared height: 70 ÷ 3.0625 = 22.86.
- Final BMI: 22.9 — in the WHO Normal category.
Healthy weight range for your height
The range is the weight interval that corresponds to a BMI of 18.5 to 24.9 at your height. At 175 cm: 18.5 × 3.0625 = 56.7 kg and 24.9 × 3.0625 = 76.3 kg, so the healthy weight range is 56.7–76.3 kg. This is a BMI-based reference range, not an individually prescribed weight target.
BMI Prime
BMI Prime compares your BMI with the reference value of 25: BMI Prime = BMI ÷ 25. A value of 1.0 sits exactly at the top of the Normal range. In the example: 22.9 ÷ 25 = 0.91.
Height-corrected BMI
The Trefethen calculation, 1.3 × weight (kg) ÷ height (m)^2.5, reduces the standard formula's tendency to overestimate BMI in tall people and underestimate it in short people. In the example it gives 22.5. It is an additional comparison figure — it does not replace BMI or provide a separate diagnosis.
Waist-to-height
When a waist measurement is entered, the page also shows your waist divided by your height. The commonly used boundary is 0.5 — at 175 cm, that means a waist under about 87.5 cm.
BMI is a screening measure, not a diagnosis. If your result is in the underweight range and you did not intend to lose weight, speak with a healthcare professional.
Examples
| Height | Weight | BMI | Category | Healthy range |
|---|---|---|---|---|
| 175 cm | 70 kg | 22.9 | Normal | 56.7–76.3 kg |
| 170 cm | 65 kg | 22.5 | Normal | 53.5–72.0 kg |
| 180 cm | 90 kg | 27.8 | Overweight | 59.9–80.7 kg |
| 165 cm | 50 kg | 18.4 | Underweight | 50.4–67.8 kg |
| 160 cm | 80 kg | 31.3 | Obesity class I | 47.4–63.7 kg |
Frequently asked questions
What is a healthy BMI?
The WHO places a BMI from 18.5 to 24.9 in the Normal range for adults. A result in this range is associated with lower health risk for most adults, but BMI is a screening measure — the category alone does not describe your overall health.
Can I use this calculator for my child?
No. Adult cut-offs do not apply to children and teenagers. For ages 2–19 the CDC uses BMI-for-age percentiles, interpreted against the CDC growth charts. Use the BMI Percentile Calculator for that age range, and ask a pediatrician to interpret growth.
Why is my BMI high even though I feel fit?
BMI does not separate muscle from fat, so a muscular person can have a high BMI with a low body-fat level. A waist measurement or a body-fat estimate can add useful context.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the Normal range. A value of 1.0 means you are at the top of that range; values above 1.0 fall in higher categories. It is a quick way to see your distance from that boundary.
What is height-corrected BMI?
The standard formula tends to classify taller people as heavier than shorter people at the same body proportions. The Trefethen adjustment (1.3 × weight ÷ height^2.5) reduces that height bias. It is shown only as a comparison figure, not as a replacement diagnosis.
Does the waist measurement change my BMI?
No. The waist field adds a separate waist-to-height line, using the commonly cited guide of keeping your waist below half your height. It does not change your BMI or your category.
Privacy and important information
RahaKit's BMI calculator runs entirely in your browser. Your height, weight and waist measurements are processed on your device; nothing you enter is sent to RahaKit's servers or stored by us. Once the page has loaded, you can keep using the calculator offline. Your measurements remain under your control.
This calculator gives estimates for information only and is not medical advice.
By Moein Shahidi, maker of RahaKit