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 Is Surface Body Area and Why Does It Matter?
Surface body area (BSA) is a measurement of your total skin surface expressed in square metres. Unlike BMI, which only considers weight and height, BSA accounts for your actual body shape and is commonly used in NHS medical practice for calculating medication doses, assessing kidney function, and determining cancer treatment protocols. Understanding your BSA can provide additional insight into your overall health profile beyond standard weight management metrics.
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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 Surface Body Area Is Calculated in UK Clinical Practice
Surface body area is calculated using your height and weight together with standardised medical formulas. The most commonly used formula in the UK is the DuBois formula, which uses both measurements to estimate skin surface in square metres (m²).
- DuBois formula: BSA = (height in cm × weight in kg)^0.5 ÷ 60
- Typical adult BSA ranges: 1.5 to 2.5 m² for most UK adults
- Clinical use: BSA is used to calculate chemotherapy doses, renal function assessment, and some other medication dosing
- Why it matters: BSA accounts for body shape variation that BMI alone cannot capture — two people with identical BMI may have different BSA values
Your GP or specialist can calculate your BSA if it's needed for your specific healthcare decisions. Use our free BMI calculator above to understand your weight category first, then discuss BSA with your healthcare provider if relevant to your treatment plan.
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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.
Surface Body Area Versus BMI — What's the Difference?
While BMI is a screening tool based only on weight divided by height squared, surface body area provides a three-dimensional assessment of your body that better accounts for muscle mass, bone density, and overall frame. For most UK adults managing their healthy weight, BMI remains the primary NHS guidance metric. However, for specific clinical situations — particularly cancer treatment, kidney disease assessment, or intensive medication protocols — BSA is more clinically accurate.
If you're focusing on weight management, our free BMI calculator and weight converter will help you track progress in UK measurements (stone, pounds, and kilograms). If your GP or specialist mentions BSA in relation to your treatment, ask them to calculate it for you as part of your personalised care plan.
- 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 do NHS doctors use surface body area for some treatments?
BSA is more accurate than BMI for calculating medication doses in cancer chemotherapy, kidney function assessment, and other specialist treatments because it accounts for actual body shape and mass distribution. Two patients with the same BMI may have different BSA values, making BSA more precise for clinical dosing. Your GP will use BSA if it's relevant to your specific condition.
What is the normal surface body area for UK adults?
Most UK adults have a BSA between 1.5 and 2.5 square metres, with average adult men around 2.0 m² and average adult women around 1.8 m². Your specific BSA depends on your individual height and weight combination. Only a healthcare professional needs to calculate this for you if it's clinically relevant.
How is surface body area different from BMI?
BMI uses only weight and height in a simple formula, while BSA accounts for the actual three-dimensional body shape using both measurements together. For healthy weight management, BMI is the standard NHS metric. BSA is primarily used in specialist clinical settings like oncology and nephrology, not for routine weight assessment.
Do I need to know my surface body area for weight management?
No — for weight management and checking if you're a healthy weight, use our free BMI calculator and NHS healthy weight guidance. Surface body area is only needed if your GP or specialist specifically requests it for treatment planning, such as chemotherapy dosing or kidney function assessment.
Can I calculate my own surface body area?
You can use the DuBois formula (height in cm × weight in kg)^0.5 ÷ 60, but your GP or specialist should calculate it officially for clinical use. For general health tracking, focus on your BMI using our free calculator and track your weight progress with our free progress tracker tool — these are the NHS-recommended metrics for weight management.
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.