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 Is 42 Kg in Stones and What's Your BMI?
42 kg is equivalent to 6 stone 8 pounds (or 6st 8lbs) in UK measurements. However, whether this is a healthy weight depends entirely on your height. BMI — a simple calculation based on your weight and height — is the key to understanding if 42 kg puts you in a healthy range according to NHS guidelines. Use our free BMI calculator above to check your personal BMI instantly, or read on to see how 42 kg translates to different BMI values at typical UK heights.
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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.
How 42 Kg Converts to BMI at Different Heights
At 42 kg, your BMI varies significantly depending on your height. Here are six common UK heights and the corresponding BMI values:
- 150 cm (4ft 11in): BMI of 18.7 — healthy weight range
- 155 cm (5ft 1in): BMI of 17.5 — healthy weight range
- 160 cm (5ft 3in): BMI of 16.4 — underweight
- 165 cm (5ft 5in): BMI of 15.4 — underweight
- 170 cm (5ft 7in): BMI of 14.5 — underweight
- 175 cm (5ft 9in): BMI of 13.7 — underweight
To convert 42 kg to stone and lbs, divide by 6.35 (the standard kg to stone conversion factor): 42 ÷ 6.35 = 6.62 stone, which equals 6 stone 8 pounds. Use our free weight converter above to switch between kilograms and stone at any time.
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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 and Limitations
NHS BMI categories for adults are: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25.0–29.9), and obese (30.0 and above). At 42 kg, most adults would fall into the underweight or healthy weight range depending on height. However, BMI has important limitations — it doesn't account for muscle mass, bone density, or where fat is stored. Athletes may have a high BMI but low body fat. If you're concerned about whether 42 kg is healthy for you personally, your GP can provide tailored advice. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds apply, so discuss this with your healthcare provider.
- 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.
Is 42 kg a healthy weight for adults?
It depends on your height. At 42 kg, you may be in the healthy weight range (BMI 18.5–24.9) if you're shorter (around 150cm or less), or underweight if you're taller. Use our BMI calculator above with your actual height to find out. Your GP can advise if 42 kg is appropriate for your individual health.
How do I convert 42 kg to stones and pounds?
42 kg equals 6 stone 8 pounds (6st 8lbs). To convert kilograms to stone, divide by 6.35. You can also use our free weight converter on this page to switch between metric and imperial measurements instantly.
What does BMI mean and why does it matter?
BMI (Body Mass Index) is a simple measure of weight relative to height. NHS uses BMI to screen for weight-related health risks. A healthy BMI is 18.5–24.9. However, BMI doesn't distinguish between muscle and fat, so it's just one health indicator. Your GP can assess your overall health alongside BMI.
Why is my BMI different from someone else at the same weight?
Because BMI depends on both weight and height. Two people weighing 42 kg but with different heights will have different BMIs. Taller people at this weight will have lower BMI scores than shorter people. This is why height is essential when calculating BMI.
What should I do if my BMI seems unhealthy?
Speak to your GP. They can assess your individual health, consider your medical history, and advise whether weight change is needed. If appropriate, they can refer you to NHS weight management services or provide guidance on sustainable lifestyle changes alongside evidence-based 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.