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
Mass Calculator — Understand Your Weight and Health
A mass calculator helps you convert your weight between different units and understand what your weight means for your health. Whether you measure yourself in kilograms, stone, or pounds, our free BMI calculator lets you instantly see your BMI category according to NHS guidelines. Combined with a weight converter tool, you can easily switch between metric and imperial measurements — essential UK health information for monitoring your weight and planning realistic health goals.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 Mass Calculators Support Weight Management
A mass calculator is a practical health tool that does three key things. First, it converts your weight between kg, stone, and pounds — the three measurement systems you're likely to encounter in UK healthcare. Second, it calculates your BMI (Body Mass Index) based on your weight and height, then compares it to NHS health categories. Third, it can estimate your healthy weight range for your height, helping you set realistic targets.
Using our free mass and BMI calculator on this page, you can:
- Convert weight instantly between any unit
- Check your personal BMI and see where it falls on the NHS scale
- Understand healthy weight thresholds for your height
- Track changes over time with our free progress tracker
This information helps you work with your GP if you're considering weight management options, whether through lifestyle changes or, for eligible adults, prescription weight loss medications like Mounjaro or Wegovy.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Why Accurate Mass Measurement Matters
Knowing your accurate weight in a format you understand is the first step in any health assessment. UK health professionals use both kg and stone, depending on context — GPs often record in kg for clinical records, but patients typically think in stone and pounds. This creates confusion. A reliable mass calculator removes that barrier and ensures you're comparing your weight correctly to NHS health thresholds.
Weight alone isn't the whole picture — your height, age, and body composition all matter. That's why our calculator includes BMI assessment and healthy weight guidance. If you're exploring weight loss support, accurate baseline measurements are essential for tracking progress fairly and spotting genuine changes versus normal fluctuation.
- 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 everyday health contexts, "mass" and "weight" are used interchangeably. Mass is the actual amount of matter in your body (measured in kg, stone, or lbs). Weight technically accounts for gravity, but on Earth, the numbers are identical. For UK health purposes, use a mass/weight calculator the same way — to measure and track your body's total measurement.
How often should I use a mass calculator?
Weigh yourself weekly at the same time of day (morning, before eating) for reliable tracking. Use the calculator once per week to monitor changes. Daily weighing can cause discouragement due to normal fluid and food fluctuations. Our free progress tracker helps you log weekly measurements and spot real trends over 4–8 weeks.
Is BMI the only thing a mass calculator should tell me?
No. A good mass calculator should also show your healthy weight range for your height (based on NHS guidelines), convert between units accurately, and note BMI limitations — it doesn't measure muscle vs. fat. For full health context, discuss your results with your GP, especially if you're considering weight management medication like Mounjaro or Wegovy.
Can I use a mass calculator if I'm on weight loss medication?
Yes. If you're taking prescription weight loss medication (such as semaglutide-based Wegovy, which is prescription-only), use your mass calculator weekly to track progress. Our GLP-1 weight loss calculator can help estimate potential outcomes, and the progress tracker lets you log actual results for your prescriber.
What should I do if my mass/BMI shows I'm overweight?
First, discuss your results with your GP. They can assess your individual health, review any weight-related conditions, and discuss options — including lifestyle changes, NHS weight management services (tier 1–3), or, if eligible, prescription treatments. Use the calculator to set realistic targets (0.5–1 kg per week is safe) and monitor progress consistently.
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.