The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
What Unit of Measure Is Used for BMI?
BMI (body mass index) uses a simple metric formula: weight in kilograms divided by height in metres squared. This standardised measurement gives a single number that helps assess whether an adult's weight falls within a healthy range. The NHS uses BMI as a screening tool for overweight and obesity, making it one of the most widely recognised health measures in the UK. Understanding the unit of measure for BMI helps you interpret your result accurately and understand what your score means for your health.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How BMI Is Calculated Using Metric Units
The BMI formula uses only two measurements:
- Weight in kilograms (kg) — your body mass
- Height in metres (m) — your height, squared (multiplied by itself)
The calculation: BMI = weight (kg) ÷ height (m)²
For example, an adult weighing 70kg and 1.73m tall would have a BMI of 70 ÷ (1.73 × 1.73) = 23.4. This falls within the NHS healthy weight range of 18.5–24.9. Use our free BMI calculator above to instantly calculate your BMI and see where you fall within the standard NHS BMI categories. The metric system is the international standard for BMI calculation, which is why the NHS and all UK health services use kilograms and metres, rather than stone, pounds, or feet and inches.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
BMI Categories and NHS Healthy Weight Ranges
Once calculated using the kg and metres formula, your BMI score is then placed into one of five categories recognised by the NHS. A healthy BMI is 18.5–24.9. Overweight is 25.0–29.9. Obesity Class I is 30.0–34.9. Class II obesity is 35.0–39.9. Severely obese (Class III) is 40.0 and above. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower BMI thresholds because these groups face higher health risks at the same weight. If you want to understand your personal healthy weight range in stone and pounds, convert your target BMI using our weight converter alongside the BMI calculator to see what your healthy weight range means in UK measurements.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Why does BMI use kilograms and metres instead of stone and pounds?
The metric system (kilograms and metres) is the international scientific standard. The NHS uses metric units in all clinical settings for consistency and accuracy. Although UK adults often think in stone and pounds, healthcare professionals use kg for medical measurements. You can convert your weight to kg using our weight converter.
Can I calculate BMI using stone and pounds instead of kg?
Yes, the Imperial formula is: (weight in pounds × 703) ÷ height (inches)². However, the metric version is simpler and more accurate. Our free BMI calculator on this page works with both metric and Imperial units, so you can enter your weight in stone and get an accurate result instantly.
What if the BMI formula doesn't account for muscle mass?
You're right — BMI has limitations. It doesn't distinguish between muscle and fat. Athletes may have a high BMI but low body fat. BMI is a screening tool, not a diagnostic measure. For a fuller picture, ask your GP about waist circumference measurements or body composition analysis alongside BMI.
Are NHS BMI categories the same for all ethnic groups?
No. The NHS recommends lower BMI thresholds for South Asian, Chinese, Black African, and Black Caribbean adults (healthy weight: 18.5–22.9 instead of 18.5–24.9) because these groups have higher disease risk at the same BMI. Check the ethnicity-adjusted thresholds with your GP for personalised guidance.
What's a healthy BMI range for me using the standard metric formula?
The healthy range is 18.5–24.9 for most UK adults. To find your personal healthy weight range in kg, multiply 18.5 and 24.9 by your height in metres squared. For example, at 1.73m, the healthy range is approximately 55–75kg (8st 8lbs to 11st 11lbs). Use our BMI calculator above to check your exact range instantly.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.