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's 13 Stone 11 Pounds in Kilograms and What's Your BMI?
13 stone 11 pounds equals approximately 87.5 kg. However, whether this weight is healthy depends entirely on your height. BMI is calculated using both weight and height together, so the same weight can give a very different BMI depending on how tall you are. Use our free BMI calculator above to find your exact BMI instantly, or read on to see how 87.5 kg translates across common UK heights and what NHS category each falls into.
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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.
BMI at Different Heights for 13 Stone 11 Pounds
At 13 stone 11 pounds (87.5 kg), your BMI varies significantly depending on height. Here's what your BMI would be at common UK heights:
- 5ft 4in (163 cm): BMI of 34.9 — falls in the Obese (Class I) category
- 5ft 6in (168 cm): BMI of 31.0 — falls in the Obese (Class I) category
- 5ft 8in (173 cm): BMI of 27.6 — falls in the Overweight category
- 5ft 10in (178 cm): BMI of 24.6 — falls in the Healthy weight category
- 6ft 0in (183 cm): BMI of 22.3 — falls in the Healthy weight category
This demonstrates why height matters so much when interpreting weight. The same 87.5 kg can represent anything from obesity to healthy weight depending on your stature. Use the weight converter on this page to check kg to stone conversions, and our BMI calculator to find your personal BMI instantly.
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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.
NHS BMI Categories and Important Limitations
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the healthy range is 18.5 to 22.9, as these groups face higher health risks at the same BMI levels.
However, BMI has important limitations — it doesn't distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI despite low body fat. BMI also doesn't account for where fat is stored (waist circumference matters too) or age-related muscle loss. For personalised advice about your weight and health, speak to your GP, who can consider your full health picture, not just BMI alone.
- 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.
How do I convert 13 stone 11 pounds to kilograms exactly?
Multiply the stone by 6.35029 and the pounds by 0.453592, then add them together. 13 × 6.35029 = 82.55 kg, plus 11 × 0.453592 = 4.99 kg, equals 87.54 kg total. You can use our free weight converter to do this instantly.
Is 13 stone 11 pounds a healthy weight?
It depends on your height. At 5ft 4in it's obese (BMI 34.9); at 5ft 8in it's overweight (BMI 27.6); at 5ft 10in it's healthy (BMI 24.6). Use our BMI calculator to find your exact category based on your personal height.
What's the healthy weight range for my height?
Healthy BMI (18.5–24.9) ranges vary by height. At 5ft 8in, healthy weight is roughly 55–74 kg (8st 9lbs to 11st 9lbs). At 5ft 10in, it's 59–79 kg (9st 4lbs to 12st 6lbs). Your GP can advise on a target range for your individual health.
Does 87.5 kg mean I'm overweight?
Not necessarily. 87.5 kg is considered overweight or obese at shorter heights, but healthy weight at taller heights. BMI is a screening tool that needs your height to be meaningful. Our BMI calculator shows you exactly where you fall.
Can I lose weight healthily from 13 stone 11 pounds?
Yes. The NHS recommends losing 0.5–1 kg per week through a calorie deficit and increased physical activity. If you're interested in prescription weight loss support, your GP can discuss options. Try our GLP-1 weight loss calculator to explore potential outcomes with medical support.
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.