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 BMI Is 13.9 Kg in Stone?
13.9 kg converts to 2 stone 3 pounds in UK measurements. However, your BMI depends entirely on your height — the same weight gives very different BMI results depending on how tall you are. This guide shows you what BMI 13.9 kg produces at common UK heights, using the NHS BMI categories. Use our free BMI calculator above to check your personal BMI instantly based on your exact height and weight.
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.
BMI for 13.9 Kg at Different Heights
13.9 kg is a relatively low body weight, typically associated with young children or very petite adults. Here's what BMI this weight gives at various heights:
- 150 cm (4ft 11in): BMI = 6.2 — Severely underweight (NHS category: Below 18.5 is underweight)
- 155 cm (5ft 1in): BMI = 5.8 — Severely underweight
- 160 cm (5ft 3in): BMI = 5.4 — Severely underweight
- 165 cm (5ft 5in): BMI = 5.1 — Severely underweight
- 170 cm (5ft 7in): BMI = 4.8 — Severely underweight
- 175 cm (5ft 9in): BMI = 4.5 — Severely underweight
At all adult heights, 13.9 kg falls well below the healthy weight range. This weight is typically only normal for infants and very young children.
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.
Understanding BMI Categories and Limitations
The NHS defines a healthy BMI as 18.5 to 24.9 for most UK adults. 13.9 kg is significantly below this range. However, BMI has important limitations — it doesn't distinguish between muscle and fat, nor does it account for bone density, age, or body composition. For adults, a weight this low warrants discussion with your GP to rule out underlying health concerns. Our free weight converter above helps you switch between kg, stone, and pounds instantly for any weight comparison.
- 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 13.9 kg to stone and pounds?
Divide 13.9 kg by 6.35029 to get stone (2.19 stone), or multiply by 2.20462 to get pounds (30.6 lbs). In UK format, 13.9 kg equals approximately 2 stone 3 pounds. Use the weight converter on this page to calculate instantly between any units.
Is 13.9 kg a healthy weight for an adult?
No. 13.9 kg is significantly underweight for any adult at any height. A healthy weight for adults starts around 45–65 kg depending on height and body composition. If you or someone you know weighs 13.9 kg, speak to your GP for health assessment.
What BMI would 13.9 kg give me?
Your BMI depends on your height. At average UK heights, 13.9 kg produces a BMI between 4.5 and 6.2 — all severely underweight. Use our free BMI calculator on this page to calculate your exact BMI for your personal height and weight.
What is the healthy weight range according to NHS guidelines?
The NHS recommends a healthy BMI of 18.5 to 24.9. For a person 170 cm tall, this equals roughly 53–72 kg (8st 5lbs to 11st 4lbs). For adults of South Asian or Chinese heritage, the NHS recommends lower thresholds starting at BMI 18.5 to 22.9.
Should I be concerned if I weigh 13.9 kg?
If you are an adult weighing 13.9 kg, this is significantly below healthy ranges and requires urgent GP consultation to identify any underlying medical cause. If this is a child's weight, use the NHS Healthy Weight Calculator for children instead, as adult BMI categories don't apply.
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.