How to Calculate BMI (WHO): A Step-by-Step Guide

Updated 5 Oct 2026 in Health & Fitness

Calculates BMI with the international WHO categories.

Health numbers are most useful when you track them consistently. A quick calculation turns everyday measurements into something you can act on, whether that is planning meals, training for a run or preparing for a clinic visit.

What you need

• Weight (kg)
• Height (cm)

Step by step

1. Enter the weight (kg).
2. Enter the height (cm).
3. The results update as you type, or press Calculate.
4. Read the bmi first, then the supporting figures below it.

The formula

BMI = kg ÷ m².

Worked example

For example, with these inputs:

• Weight (kg): 68
• Height (cm): 170

the calculator returns:

• BMI: 23.53
• WHO category: Normal weight

A second example

Now change the inputs to:

• Weight (kg): 85
• Height (cm): 170

the calculator returns:

• BMI: 29.41
• WHO category: Overweight

Practical tips

• Measure at the same time of day, ideally in the morning, for consistent readings.
• Small, steady changes are easier to sustain than dramatic targets.
• Track trends over weeks rather than reacting to a single reading.
• Healthy 365 and wearables give useful data, but treat their calorie figures as approximate.

Background

Simple measurements such as weight, height and waist circumference are widely used to screen for health risks because they are cheap and easy to repeat. They are not diagnoses, but tracked over time they show whether lifestyle changes are working.

Programmes such as the National Steps Challenge and the Healthy 365 app have made tracking activity common. Turning those numbers into distance, pace or calories helps set realistic goals for events like IPPT or a 10 km run.

Singapore's tropical climate means you lose more fluid through sweat, even when you are not exercising. Thirst, urine colour and how you feel are good guides, and needs rise during outdoor activity or heat waves.

Related calculations

• Running Pace Calculator: Calculates pace for runs like the Standard Chartered Marathon or IPPT 2.4 km.
• Calories Burned Calculator: Estimates calories burned with MET values.
• BMI Calculator (Asian Cut-offs): Singapore's Health Promotion Board uses lower BMI cut-offs for Asians because health risks rise at lower BMIs.
• BMR Calculator: Estimates calories your body burns at rest.

Want to skip the arithmetic? The free BMI Calculator (WHO) does all of this instantly and updates as you type.

Run your own numbers: BMI Calculator (WHO)