Body Mass Index (BMI) is the single number clinicians, insurers, and public-health researchers have used for nearly two centuries to summarize the relationship between your weight and your height. This metric BMI calculator is built specifically for the way most of the world measures its body: height in centimeters on a stadiometer, and weight in kilograms on a digital scale. There are no feet, no inches, no pounds, and no unit switchers to fumble with — just two numbers and an instant result.
Type in your height in cm and your weight in kg, and the tool computes your BMI, the WHO/NIH weight category you fall into, the healthy weight band for your exact height, your target weight at a chosen goal BMI, and how many kilograms you would need to gain or lose to reach that goal.
How to Use
- Stand against a wall without shoes and measure your Height in centimeters. For most adults this is between 150 cm and 195 cm. Enter it in the Height box, for example
175. - Weigh yourself on a calibrated scale, first thing in the morning and lightly clothed, and enter the result as Weight in kilograms, for example
70. - Set your Target BMI (optional). The default is 24.9, the WHO upper edge of the Normal band. If you have a personal goal — say 22.5, a mid-normal BMI many people aim for — type it in and the target-weight line updates live.
- Read your BMI on the result card. A value around 22–23 is typical for an adult at a healthy weight.
- Check the BMI Category code (1 = Underweight, 2 = Normal, 3 = Overweight, 4 = Obese). The same number means a different clinical tier depending on which WHO threshold it crosses.
- Look at the Healthy Weight range for your height. It is the weight band that keeps your BMI between 18.5 and 24.9.
- Use the Target Weight at Goal BMI and Weight to Gain/Loss lines. A negative number means how many kg you need to lose to hit your goal; a positive number means how many kg you need to gain.
The Metric BMI Formula
The BMI was devised by the Belgian statistician Adolphe Quetelet in the 1830s and adopted as the standard population measure by the World Health Organization. In its pure metric form it is deliberately simple:
BMI = weight (kg) ÷ height (m)²
Because scales and stadiometers give centimeters rather than meters, the calculator converts for you: it divides your height in cm by 100, squares it, and divides your weight in kilograms by that squared value.
Worked example: a 70 kg adult who is 175 cm tall. Height in meters is 1.75 m; squared it is 1.75 × 1.75 = 3.0625. BMI = 70 ÷ 3.0625 = 22.9, which lands squarely in the Normal band. The healthy weight range for this height runs from 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg.
WHO/NIH Adult Weight Categories
The cutoffs are fixed for all adults aged 20 and over, regardless of sex:
- Underweight — BMI below 18.5.
- Normal — BMI from 18.5 up to 24.9.
- Overweight — BMI from 25.0 up to 29.9.
- Obese — BMI of 30.0 or higher.
Public-health guidance holds that shedding just 5% to 10% of starting body weight already measurably improves blood pressure, cholesterol, and blood-sugar markers. If your result sits in the Overweight band, aim first for that modest 5%–10% reduction rather than a target weight from a decade ago.
Examples
Example 1 — The reference adult. Height 175 cm, weight 70 kg, target BMI 24.9. BMI = 70 ÷ 1.75² = 22.9, Normal (category 2). The healthy band is 56.7–76.3 kg. At a target BMI of 24.9, the target weight is 76.3 kg, so the weight-to-target line shows +6.3 kg — meaning this person would need to gain 6.3 kg to reach the upper edge of normal; at their current 22.9 they are already well inside the healthy band.
Example 2 — Overweight by a small margin. Height 170 cm, weight 80 kg, target BMI 24.9. Height squared is 2.89; BMI = 80 ÷ 2.89 = 27.7, Overweight (category 3). The target weight at BMI 24.9 is 24.9 × 2.89 = 72.0 kg, so the weight-to-target line shows −8.0 kg to lose — a realistic 3- to 6-month goal through diet and walking.
Example 3 — Underweight. Height 165 cm, weight 50 kg, target BMI 24.9. Height squared is 2.7225; BMI = 50 ÷ 2.7225 = 18.4, Underweight (category 1). The healthy band starts at 18.5 × 2.7225 = 50.4 kg, so gaining just 0.4 kg would move this adult into Normal (category 2). The target weight at BMI 24.9 is 67.8 kg, which is the full upper-band goal, not the minimum to cross into Normal.
Example 4 — Custom personal target. Same 70 kg, 175 cm adult but with a target BMI of 22.5 (a common mid-normal personal goal). The target weight becomes 22.5 × 3.0625 = 68.9 kg, and the weight-to-target line shows −1.1 kg — a small downward nudge rather than a large cut.
FAQ
How do I calculate my BMI in metric units?
Divide your weight in kilograms by your height in meters squared. First divide your height in centimeters by 100 to get meters (for example 175 cm = 1.75 m), square that number, then divide your kg by the result. For 70 kg and 1.75 m: 70 ÷ (1.75 × 1.75) = 22.9.
What is a healthy BMI range for adults?
The WHO and NIH define the Normal range as BMI 18.5 to 24.9. Below 18.5 is Underweight, 25.0 to 29.9 is Overweight, and 30.0 and above is Obese. These adult cutoffs apply to men and women aged 20 and over and do not change with age.
Is BMI accurate for everyone?
BMI is a population screening tool, not a body-fat measurement. It cannot distinguish muscle from bone from fat, so a very muscular athlete may read Overweight while being lean, and an older adult who has lost muscle may read Normal while carrying excess fat. It is best used as a rough trend line over months and years, alongside waist circumference and blood tests.
Should I use cm or m in this calculator?
Enter height in centimeters — that is the unit this tool expects. The conversion to meters (cm ÷ 100) happens automatically inside the formula, so there is no need to divide by 100 yourself.
How much weight should I lose to reach a normal BMI?
The result card shows a Target Weight at Goal BMI and a Weight to Gain/Loss line. The default goal BMI is 24.9 (the WHO upper edge of Normal), but you can type in any target between 15 and 40 — for example 22.5 for a mid-normal personal goal. A negative figure means kg to lose; a positive figure means kg to gain. Keep in mind that a loss of just 5% to 10% of your starting weight already delivers meaningful health gains, so you do not need to hit the middle of the healthy band to benefit.
Does BMI work for children and teenagers?
No. The fixed 18.5 / 25 / 30 cutoffs are for adults only. Children and adolescents are assessed with age- and sex-specific BMI-for-age percentiles, so use a pediatric BMI calculator for anyone under 20.
Disclaimer
This metric BMI calculator is provided for informational purposes only and is not medical advice. BMI is a rough screening measure and does not diagnose body fat percentage, disease, or fitness. Results depend on the accuracy of the height and weight you enter and on the standard WHO/NIH adult cutoffs. Always discuss your weight, diet, and activity levels with a qualified doctor or registered dietitian before making changes based on this result.