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 Basal Surface Area?
Basal surface area (BSA) is a measurement of your total skin surface area, calculated from your height and weight. It's used in UK healthcare to help determine safe medication doses, assess nutritional needs, and support clinical decision-making. Understanding your BSA can give you valuable insight into how your body is assessed by healthcare professionals and why it matters for personalised health guidance.
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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 is Basal Surface Area Calculated?
BSA is calculated using your height and weight in a mathematical formula. The most common formula used in UK clinical practice is the DuBois formula:
- BSA (m²) = 0.007184 × height (cm)^0.725 × weight (kg)^0.425
For example, an adult who is 170cm tall and weighs 70kg would have a BSA of approximately 1.84 m². Other formulas exist, such as the Mosteller formula, which is simpler but slightly less precise. Your GP or healthcare professional can calculate your BSA, or you can use online health calculators for an estimate. BSA is typically expressed in square metres (m²). Understanding your BSA helps healthcare professionals tailor treatments and medications to your individual body composition rather than using one-size-fits-all dosing.
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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.
Why Does Basal Surface Area Matter in Healthcare?
BSA is particularly important in medication dosing, especially in oncology, chemotherapy, and specialist weight management. Many prescription medications—including certain weight loss injections—are dosed based on BSA rather than weight alone, because this accounts for how your body metabolises drugs. BSA is also used to assess nutritional requirements, calculate metabolic rate, and evaluate kidney and liver function. In the context of weight management and health assessment, BSA gives clinicians a more nuanced picture of your body composition than weight or BMI alone, supporting more personalised clinical decisions alongside BMI calculator assessments and UK NHS health guidance.
- 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.
Is basal surface area the same as body mass index (BMI)?
No. BMI is calculated from weight and height to screen for weight-related health risks. BSA measures your total skin surface area for medication dosing and metabolic assessment. Both are useful in UK healthcare but serve different purposes. Use our BMI calculator to check your personal BMI, and your GP can calculate your BSA.
Can I calculate my basal surface area at home?
You can estimate your BSA using online calculators with your height and weight, but clinical BSA calculations should be done by your GP or healthcare professional to ensure accuracy. Results are typically expressed in square metres (m²). For clinical decisions, always confirm with your prescriber.
How is basal surface area used in weight management?
In weight management, BSA helps healthcare professionals assess your metabolic needs and determine appropriate medication dosing. Some weight loss medications are dosed based on BSA rather than weight alone. Your GP will consider BSA alongside your BMI, health history, and other factors when recommending treatment options.
What is a normal basal surface area?
Normal BSA for UK adults ranges from approximately 1.5 to 2.0 m², depending on height and weight. Most adults fall between 1.7 and 1.9 m². BSA increases with body size but doesn't scale linearly with weight, so two people of the same weight can have different BSA values depending on height.
Does basal surface area change if I lose weight?
Yes. As you lose weight, your BSA decreases because your total skin surface area reduces. This is why medication doses may need adjustment during weight loss treatment. If you're using a weight loss calculator or tracking weight loss with our progress tracker, your BSA will change proportionally as your weight changes.
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.