Step 01
Understand the formula.
BMI = weight in kilograms ÷ height in metres squared. The calculator accepts metric or imperial inputs and converts them before the calculation.
The healthy-weight range shown uses the common 18.5–24.9 screening band for adults.
Step 02
Worked example: 70 kg at 175 cm.
1.75 metres squared is 3.0625. Dividing 70 by 3.0625 gives a BMI of about 22.9, which falls in the healthy-weight range.
The healthy range for that height is roughly 56.7–76.3 kg under the same band.
Step 03
Remember what BMI does not measure.
BMI is a screening figure that can help start a conversation. It is not a complete health assessment and should not be used alone to judge someone's health.
- Muscle mass versus body fat.
- Age, sex and ethnicity differences in risk.
- Where fat is distributed on the body.
- Fitness, diet, medical history or individual health.
Step 04
Use the result appropriately.
Record the inputs and result in the worksheet, then discuss anything concerning with a clinician. For children and teenagers, adult BMI bands do not apply in the same way.
This guide is general health information, not medical advice.
Free reusable resource
Keep a practical worksheet.
Download a blank, editable file and keep the plan with your own records. No email address is required.
BMI screening worksheet
Record weight, height, BMI, category and healthy range together with the context notes that matter for interpretation.
Sources and further guidance
References used for this guide.
How do I measure my Body Mass Index (BMI)?
NHS inform. NHS inform explains BMI measurement, healthy ranges and the limitations of BMI as a screening tool.