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
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What's 12.3 Kg in Stone? BMI at Different Heights
12.3 kg converts to approximately 1 stone 13.3 lbs (or just under 2 stone) in UK measurements. However, your BMI — which indicates whether this weight is healthy for you — depends entirely on your height. The same weight can be a healthy BMI for a taller person but overweight or obese for someone shorter. Use our free BMI calculator above to check your personal BMI instantly, or read on to see example BMI values at different heights for 12.3 kg.
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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 12.3 Kg
At 12.3 kg, your BMI varies significantly depending on your height. Here are example BMI values at common adult heights:
- 150 cm (4ft 11in): BMI = 54.7 — Severely obese (Class III)
- 160 cm (5ft 3in): BMI = 47.9 — Severely obese (Class III)
- 170 cm (5ft 7in): BMI = 41.6 — Severely obese (Class III)
- 175 cm (5ft 9in): BMI = 40.0 — Severely obese (Class III)
- 180 cm (5ft 11in): BMI = 37.9 — Obese (Class II)
- 190 cm (6ft 3in): BMI = 34.0 — Obese (Class I)
Note: 12.3 kg is an extremely low weight for an adult. If this represents your current weight, please contact your GP for health support, as this may indicate malnutrition or an underlying health condition.
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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 Limitations
NHS BMI categories for adults are: Underweight (below 18.5), Healthy weight (18.5–24.9), Overweight (25.0–29.9), Obese Class I (30.0–34.9), Obese Class II (35.0–39.9), and Severely obese (40.0+). For people of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends lower thresholds due to higher health risks at lower BMI levels.
Remember: BMI has limitations — it doesn't distinguish between muscle and fat, and doesn't account for where fat is stored. Waist circumference is also important. Your GP can provide personalised health advice about what your weight and BMI mean for your health. Use the weight converter above to check other measurements.
- 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 12.3 kg to stone?
Divide 12.3 by 6.35029. This gives approximately 1 stone 13.3 lbs. You can use our free weight converter above for instant conversions between kg, stone, and pounds in both directions.
Is 12.3 kg a healthy weight for an adult?
No — 12.3 kg is extremely low for an adult and would result in a BMI well above 40 at most heights. This weight may indicate serious malnutrition or an underlying health condition. Please see your GP immediately for medical assessment and support.
What is the healthy weight range in kg to stone?
For a person 5ft 8in (173 cm) tall, the healthy BMI range (18.5–24.9) equals approximately 8 stone 12 lbs to 11 stone 10 lbs (55–75 kg). Use our free BMI calculator to find the healthy weight range for your specific height.
Does my BMI change if I'm of South Asian or Black heritage?
Yes. The NHS recommends lower BMI thresholds for people of South Asian, Chinese, Black African, and Black Caribbean heritage because these groups face higher health risks at lower BMI levels. A healthy BMI for these groups is 18.5–22.9 rather than 18.5–24.9. Discuss this with your GP.
What should I do if I'm significantly underweight?
If you weigh 12.3 kg or are significantly underweight, contact your GP or NHS 111 for urgent advice. Underweight status can indicate malnutrition, eating disorders, or serious underlying health conditions. Your GP can assess your individual situation and provide appropriate 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.