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
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How to Compute Mass — A UK Health Guide
Computing mass — or calculating weight — is straightforward once you understand the units and formulas involved. In the UK, we use kilograms (kg), stone, and pounds (lbs) to measure body weight, and each unit requires different conversion methods. Whether you're tracking your weight for health reasons, preparing for a GP appointment, or using NHS guidance to assess your healthy weight range, knowing how to compute and convert mass is essential. This guide explains the main methods and shows you how to use them in a UK health context.
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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 to Calculate and Convert Mass in UK Measurements
Mass and weight are often used interchangeably in everyday UK health discussions, though technically mass is measured in kilograms and weight accounts for gravity. For health purposes, we focus on mass in kilograms.
Key conversion formulas:
- Kilograms to stone: divide kg by 6.35029 (example: 70 kg ÷ 6.35 = 11 stone)
- Kilograms to pounds: multiply kg by 2.20462 (example: 70 kg × 2.20 = 154 lbs)
- Stone to kilograms: multiply stone by 6.35029
- Stone to pounds: multiply stone by 14 exactly
These standard conversion factors are used across NHS health services and UK weight management guidance. Rather than calculating manually, you can use our free weight converter above to instantly switch between all three units — it's faster and eliminates rounding errors.
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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.
Computing Mass for NHS Health Assessment
Once you've computed your mass in kilograms, the NHS uses this figure to calculate your BMI (body mass index), which determines whether your weight falls into a healthy range. For adults, a healthy BMI is 18.5 to 24.9; your GP may discuss your individual health risk based on this figure and other factors like waist measurement.
Our free BMI calculator on this page computes your BMI instantly and shows you where you fall on the NHS weight categories. If you're interested in weight loss or weight management, our GLP-1 weight loss calculator can help you explore projected outcomes. Your GP remains your best resource for personalised advice about your weight and health.
- 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.
What's the difference between mass and weight in UK health terms?
In everyday UK health language, "mass" and "weight" are used interchangeably. Mass is measured in kilograms and technically refers to the amount of matter in an object. Weight includes gravity's effect, but for health purposes we measure mass in kg using the same scales. NHS guidance and BMI calculations all use mass in kilograms.
How do I convert 80kg to stone?
Divide 80 by 6.35029. The result is approximately 12 stone 8 pounds. Use our free weight converter on this page to convert any kilogram value instantly to stone and pounds without a UK pharmacy calculation.
Why does the NHS use kilograms instead of stone?
Kilograms are the standard scientific unit across healthcare systems globally, making clinical data consistent and comparable. However, the NHS understands that UK adults prefer stone for personal weight discussions, so healthcare professionals use both units depending on context.
Can I compute my healthy weight range myself?
Yes. Multiply your height in metres by itself, then multiply by 18.5 for the lower healthy weight and by 24.9 for the upper limit. For example, at 1.73m: lower = 55.4 kg, upper = 74.5 kg. Your GP can also advise on your individual healthy weight range based on your health history.
What should I do after I've computed my BMI?
If your BMI falls outside the healthy range (18.5–24.9), speak to your GP about weight management options. Even a 5% reduction in body weight can improve health markers. Your GP can discuss lifestyle changes, NHS weight management services, or other support available in your area.
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.