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
Understanding Body Surface Area — A UK Health Guide
Body surface area (BSA) is a measurement used in UK healthcare to calculate the total area of skin covering your body. Unlike simple weight or height measurements, BSA provides a more accurate basis for determining drug doses, nutritional requirements, and assessing health status in clinical settings. Understanding your BSA can help you engage more meaningfully with your GP or healthcare team about personalised treatment recommendations.
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.
What Is Body Surface Area and Why Does It Matter?
Body surface area is measured in square metres (m²) and represents the total external area of the human body. It's calculated using your height and weight, making it more accurate than weight alone for determining safe medication doses — particularly important in cancer treatment, heart disease management, and specialist therapies.
In UK healthcare, BSA is especially relevant for:
- Calculating chemotherapy and cancer drug doses — safety depends on precise BSA measurement
- Determining safe doses for certain heart and kidney medications
- Assessing burn severity in emergency medicine
- Evaluating nutritional needs in critical care
- Monitoring growth and development in children
The most commonly used BSA formula in UK clinical practice is the Mosteller formula, which uses height (in cm) and weight (in kg). Your GP or specialist can calculate your BSA, or you can use our free BMI calculator above which provides BSA context alongside weight assessment.
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.
How to Calculate Your Body Surface Area
The standard Mosteller formula is: BSA (m²) = √(height in cm × weight in kg ÷ 3,600)
For most UK adults, BSA ranges from approximately 1.5 to 2.5 m². A typical adult woman with a height of 163cm (5ft 4in) and weight of 65kg has a BSA of around 1.75 m². An average adult man at 178cm (5ft 10in) and 85kg has approximately 2.05 m².
If you're being prescribed specialist medications or undergoing cancer treatment, your NHS healthcare team will calculate your exact BSA using your precise measurements. This ensures dosing is safe and effective for your individual physiology. Use our weight converter to check your weight in kg if you're familiar with stone and pounds.
- 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 the NHS use body surface area instead of just weight?
Weight alone doesn't account for how your height and build affect drug distribution and metabolism. A 90kg person who is 1.95m tall has very different BSA than a 90kg person who is 1.60m tall. BSA provides a more accurate, personalised measure for safe medication dosing, particularly critical for chemotherapy and high-risk drugs.
What is a normal body surface area for UK adults?
Most UK adults have a BSA between 1.5 and 2.5 m². Average UK adult men have BSA around 2.0–2.1 m², while average UK adult women have BSA around 1.8–1.9 m². Your individual BSA depends on your specific height and weight combination, not just one measurement.
Is body surface area the same as BMI?
No. BMI (body mass index) measures weight relative to height and assesses whether you're in a healthy weight range according to NHS guidelines. BSA measures your total skin surface area and is primarily used for medical drug dosing and specialist healthcare calculations. Both are useful but for different purposes.
Can I calculate my body surface area at home?
Yes, using the Mosteller formula with your height in cm and weight in kg. However, for medical purposes — especially medication dosing — always ask your GP or specialist to calculate it. They'll use your exact measurements and may use alternative formulas depending on your specific condition.
Does body surface area change with weight loss?
Yes. Your BSA will change as your weight and body composition change. If you're managing your weight through lifestyle changes or specialist weight management treatment, your BSA will be recalculated by your healthcare team to ensure medication doses remain safe and appropriate for your new measurements.
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.