How do I work out my BMI?
Peter Paumgardhen | Last update: 7th May 2025
Body Mass Index (BMI) is a widely used tool to understand your weight in relation to your height – this guide shows how you work out your BMI. It’s simple to calculate and provides a quick reference for categorising your weight — underweight, healthy weight, overweight, or obese. It’s one of the key factors your doctor, or healthcare provider, will use when deciding if you qualify for the new weight loss drugs, like Mounjaro or Wegovy.
What is BMI, and why does it matter?
BMI is a quick calculation that uses your weight and height to give you an idea of your body size. If you’re wondering how do I work out my BMI, you’re not alone — and we’re here to walk you through it.
While it doesn’t account for factors like muscle mass or distribution of fat, it’s a helpful starting point for understanding weight-related health risks.
This guide is for adults aged 18 and over. If you’re pregnant, BMI calculations may not apply to you. Consult your Doctor or healthcare provider for more accurate assessments.
How do I work out my BMI?
Good news! You only need two things to calculate your BMI:
- Your weight
- Your height
Whether you prefer metric (kilograms and centimetres) or imperial (pounds and inches), we’ve got you covered.
Step-by-step guide
For metric measurements:
- Weigh yourself: Use a scale to measure your weight in kilograms.
- Measure your height: Use a tape measure to find your height in metres. If you measure in centimetres, divide the result by 100 to convert to metres.
- Apply the formula: Divide your weight by your height squared (weight ÷ height²).
Example:
- Weight: 70kg
- Height: 1.75m
- BMI = 70 ÷ (1.75 × 1.75) = 22.86
For imperial measurements:
- Weigh yourself: Record your weight in pounds.
- Measure your height: Measure your height in inches.
- Apply the formula: Multiply your weight by 703, then divide by your height squared (weight × 703 ÷ height²).
Example:
- Weight: 154lbs
- Height: 68 inches
- BMI = (154 × 703) ÷ (68 × 68) = 23.41
Tip: Not great with numbers? Use the NHS BMI Calculator for an easy way to calculate it.
Understanding BMI calculation categories
Once you’ve calculated your BMI, it’s time to interpret the results. Here are the general categories:
- Underweight: BMI below 18.5
- You may need to focus on gaining weight for better health.
- Healthy weight: BMI between 18.5 and 24.9
- This is considered the ideal range for most people.
- Overweight: BMI between 25 and 29.9
- While not necessarily unhealthy, this range may indicate increased health risks.
- Obese: BMI of 30 or above
- Higher BMIs in this range often correlate with significant health risks, and medical intervention might be advised.
BMI and GLP-1 weight-loss drugs
If your BMI falls into the overweight or obese categories, you may be wondering about using weight-loss drugs. BMI is one of the key criteria for determining eligibility for these treatments? Learn more about the BMI requirements and additional factors in our article, ‘What eligibility criteria must you meet to get weight-loss drugs on prescription?’
BMI isn’t perfect! Even for athletes!!
While BMI is a helpful guide, it’s not perfect. It doesn’t differentiate between fat and muscle, so athletes or muscular individuals might have higher BMIs even though they’re in excellent health. Additionally, BMI doesn’t account for factors like your age, gender, or fat distribution.
Always consult your doctor or healthcare provider for advice for your individual health needs.
Still wondering how do I work out my BMI or how it relates to your weight loss plan? Share your questions and tips in the SlimrChat forums — or just browse what others are saying.