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
21 Stone to Kg — Quick Conversion & Health Context
21 stone is equal to 133.36 kilograms. This weight falls into the obese category according to NHS guidelines for most UK adults. Understanding your weight in both stone and kilograms is helpful for health assessments, medical appointments, and using international health tools. Use our free weight converter above to switch between metric and imperial measurements instantly, and our BMI calculator to see how this weight relates to your height and overall health status.
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 to Convert 21 Stone to Kilograms
To convert 21 stone to kg, multiply the stone value by 6.35029. The calculation is: 21 × 6.35029 = 133.36 kg. This metric to imperial weight conversion works because 1 stone equals exactly 6.35029 kilograms.
The reverse calculation (kg to stone) divides by 6.35029: 133.36 ÷ 6.35029 = 21 stone. For quick reference, use our free weight converter above for instant conversions between stone and pounds, kilograms, and pounds.
Here are nearby values for reference:
- 20 stone = 127.01 kg
- 20.5 stone = 130.18 kg
- 21 stone = 133.36 kg
- 21.5 stone = 136.53 kg
- 22 stone = 139.71 kg
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.
Is 21 Stone Overweight or Obese?
At 21 stone (133.36 kg), your BMI category depends on your height. For an average UK adult male height of 5ft 9in (175 cm), 21 stone gives a BMI of approximately 38, which falls into the obese (Class II) category according to NHS guidelines. For women at average UK height of 5ft 3in (160 cm), the same weight gives a BMI of around 42 (severe obesity).
Use our free BMI calculator above to find your personal BMI based on your exact height and weight. The NHS recommends a healthy weight range of 18.5–24.9 BMI. Losing even 5–10% of body weight can improve health markers including blood pressure and blood sugar control.
- 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 is 21 stone in kilograms?
21 stone equals 133.36 kilograms. To convert, multiply 21 by 6.35029 (the conversion factor from stone to kg). This is the standard metric conversion used by NHS health professionals and international health assessments.
How do I convert stone to kilogram weight?
Multiply the stone value by 6.35029 to get kilograms. For example: 21 stone × 6.35029 = 133.36 kg. To convert kilograms back to stone, divide by 6.35029. Our free weight converter above performs these calculations instantly for any weight value.
What is a healthy weight in kilograms for UK adults?
A healthy BMI (18.5–24.9) corresponds to different weights depending on height. For a 175cm (5ft 9in) adult, healthy weight is roughly 56–75kg. For a 160cm (5ft 3in) adult, it's roughly 47–64kg. Use our BMI calculator to find the healthy weight range for your specific height.
Is 21 stone considered obese?
Yes, at 21 stone (133.36kg), most UK adults would be classified as obese or severely obese depending on height. For average UK heights, this weight typically gives a BMI above 35, placing it in the obese or severe obesity category. Your GP can provide personalised health assessment.
Can I track my weight loss from 21 stone?
Yes. Use our free progress tracker to log your weight over time in stone, kilograms, or pounds — whatever units you prefer. Regular tracking helps visualise progress and can be motivating. Sustainable weight loss is typically 0.5–1kg per week alongside diet and physical activity 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.