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 13.5 Kg in Stone and What's the BMI?
13.5 kilograms converts to 2 stone and 2.2 pounds (or 2.13 stone exactly). However, your BMI depends entirely on your height — the same weight can be a healthy BMI for a tall adult or overweight for someone shorter. Use our free BMI calculator above to find your personal BMI, or see how 13.5kg affects different heights below. This guide explains the NHS BMI categories and helps you understand what your weight means for your health.
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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.
13.5 Kg BMI at Different Heights
13.5kg is a very light weight for most adults, but BMI context matters. Here's how 13.5kg converts to BMI across typical adult heights:
- 150cm (4ft 11in): BMI 6.0 — severely underweight
- 160cm (5ft 3in): BMI 5.3 — severely underweight
- 170cm (5ft 7in): BMI 4.7 — severely underweight
- 180cm (5ft 11in): BMI 4.2 — severely underweight
At any realistic adult height, 13.5kg falls far below the NHS healthy weight range of 18.5–24.9 BMI. This weight is extremely low for a fully-grown adult. If you weigh 13.5kg or are concerned about being underweight, speak to your GP about your health. Use our weight converter to check how kilograms to stone conversion works, and the BMI calculator to assess your personal situation.
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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 Health Context
According to NHS guidelines, a healthy BMI is 18.5 to 24.9 for most adults. BMI categories are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), obese (30.0–34.9), and severely obese (40.0+). For South Asian, Chinese, Black African, and Black Caribbean adults, NHS recommends lower thresholds because these groups face higher health risks at lower BMI levels.
Important: BMI does not account for muscle mass, bone density, or where fat is stored. A muscular person may have a high BMI but good health, whilst BMI alone doesn't assess overall fitness. Your GP can provide personalised health advice beyond BMI.
- 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 13.5 kilograms in stone and pounds exactly?
13.5kg converts to 2 stone and 2.2 pounds, or 2.13 stone in decimal form. To convert kilograms to stone, divide by 6.35029. Use our free weight converter on this page to switch between kg, stone, and pounds instantly for any weight.
Is 13.5 kg a healthy weight for an adult?
13.5kg is extremely light for any adult height and would indicate severe underweight status. Healthy adult weights typically range from around 45kg (7 stone) to 100kg+ depending on height. If you weigh 13.5kg or are concerned about being underweight, consult your GP about your nutrition and health.
How do I calculate my BMI if I weigh 13.5 kg?
BMI = weight (kg) ÷ height (metres)². For example, at 170cm tall, 13.5kg gives BMI 4.7. Use our free BMI calculator above to find your exact BMI instantly by entering your weight and height — it works for any weight and height combination.
What does underweight mean according to the NHS?
The NHS defines underweight as BMI below 18.5. This can indicate inadequate nutrition, certain medical conditions, or other health concerns. Being significantly underweight carries health risks including weak bones, weakened immunity, and muscle loss. Speak to your GP if you're underweight.
Should I use stone or kg for measuring my weight in the UK?
Both are used in the UK. The NHS uses kilograms clinically, but many UK adults prefer stone and pounds for personal tracking. Use whichever feels natural — our weight converter makes it easy to switch between all three measurements (kg, stone, pounds) whenever you need to.
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.