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 Is 12.3 Kg In Pounds And Your BMI?
12.3 kg equals approximately 27.1 pounds. However, your BMI — and which NHS weight category you fall into — depends entirely on your height. This guide shows you what BMI a weight of 12.3 kg gives at different heights, and explains where that sits within NHS healthy weight ranges. Use our free BMI calculator above to find your personal BMI instantly, or check the examples below to understand how height affects your weight category.
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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.
12.3 Kg BMI At Different Heights
At 12.3 kg, your BMI varies significantly depending on your height. Here are typical examples using standard metric to imperial weight conversions:
- At 150 cm (4ft 11in): BMI = 54.7 — Severely obese (Class III)
- At 160 cm (5ft 3in): BMI = 48.1 — Severely obese (Class III)
- At 170 cm (5ft 7in): BMI = 42.3 — Severely obese (Class III)
- At 175 cm (5ft 9in): BMI = 40.2 — Severely obese (Class III)
- At 180 cm (5ft 11in): BMI = 37.9 — Obese (Class II)
- At 190 cm (6ft 3in): BMI = 34.0 — Obese (Class I)
These calculations use kilos in stone conversion principles: multiply 12.3 kg by 2.20462 to get 27.1 pounds, then divide by height squared (in metres). Important: 12.3 kg is an extremely low weight for most adults — this weight range typically only applies to young children, not adults.
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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.
Understanding NHS BMI Categories
According to NHS guidelines, BMI categories for UK adults are:
- Below 18.5 — Underweight
- 18.5–24.9 — Healthy weight
- 25.0–29.9 — Overweight
- 30.0–34.9 — Obese (Class I)
- 35.0–39.9 — Obese (Class II)
- 40.0+ — Severely obese (Class III)
BMI has limitations: it does not distinguish between muscle and fat, does not account for where fat is stored, and may be less accurate for elderly people or athletes. Your GP can provide personalised health advice. Convert your weight between kg to stone and other units using the weight converter on this page to see your measurement in different formats.
- 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 12.3 kg in pounds?
12.3 kg equals approximately 27.1 pounds. To convert kilograms to pounds, multiply by 2.20462. However, 12.3 kg is extremely low for an adult and typically only represents a newborn or young child's weight.
Is 12.3 kg a healthy weight for an adult?
No. 12.3 kg is far below any healthy weight range for adults. This weight typically represents a newborn or infant. For adults, NHS guidelines recommend a healthy BMI of 18.5–24.9, which corresponds to much higher weights depending on height. Consult your GP if you or someone you know is significantly underweight.
How do I calculate my BMI if I weigh 12.3 kg?
BMI = weight (kg) ÷ height (m)². For example, at 160 cm (1.6 m), a weight of 12.3 kg gives BMI = 12.3 ÷ (1.6)² = 48.1 (severely obese category). Use our free BMI calculator above to enter your actual height and weight for an accurate personal BMI result.
How do I convert kilos to stone?
To convert kilogrammes to stone, divide by 6.35029. So 12.3 kg ÷ 6.35 = approximately 1.94 stone (1 stone 13.2 pounds). The weight converter on this page lets you instantly switch between kg, stone, and pounds.
Should I be concerned if someone weighs 12.3 kg?
If an adult weighs 12.3 kg, this is a serious medical concern and they should see their GP immediately. If this is a child's weight, consult your health visitor or GP — they can assess whether growth and development are normal using UK90 growth charts.
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.