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 the average weight of an 8 year-old boy in kg?
The average weight of an 8 year-old boy in the UK is approximately 27–28 kg (60–62 lbs), though healthy weight varies considerably depending on height, build, and individual development. Rather than focusing on a single "ideal" weight, the NHS uses growth charts that track children's weight and height together to assess healthy development. If you're concerned about your child's weight or growth, your GP can plot your child on an NHS growth chart and provide personalised guidance based on their individual pattern of development.
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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.
Understanding children's weight in the UK context
In the UK, children's weight assessment is very different from adult health weight management. The NHS uses age and sex-specific growth reference charts (the UK90 charts) which track weight against height, not BMI categories like adults. A child's healthy weight depends on their individual growth pattern, genetics, and development stage—not a single target number.
- Age 8 average: Typically ranges from 24–32 kg depending on height and build
- Growth charts matter more than numbers: A consistent growth pattern (following the same centile line) is usually a sign of healthy development
- Height variation: An 8 year-old boy who is 120 cm tall may weigh 24 kg, while one who is 140 cm tall might weigh 35 kg—both can be perfectly healthy
- When to ask your GP: Sudden changes in growth rate, rapid weight gain, or concerns about development warrant a professional assessment
The NHS does not recommend weight loss dieting for children unless specifically advised by a healthcare professional, as growth and development are ongoing priorities.
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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.
When to speak to your GP about your child's weight
Your GP can assess your child's weight in proper context using NHS growth charts and their individual health history. Speak to your GP if you notice: a sudden change in your child's growth pattern, rapid weight gain over a short period, signs of fatigue or health problems, or if you have concerns about their overall development.
Growth is influenced by genetics, nutrition, physical activity, sleep, and individual development timing. Early intervention and supportive guidance from your healthcare team is far more helpful than self-assessment. Your GP can also signpost you to NHS healthy weight resources and family-based programmes if appropriate. Remember that childhood is a time of rapid change—growth isn't always linear, and variations are normal.
- 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 28 kg a healthy weight for an 8 year-old boy?
Weight alone doesn't determine if a child is healthy. The NHS uses growth charts that plot weight against height and age. A child weighing 28 kg could be perfectly healthy or not—it depends on their height, build, and growth pattern. Your GP can assess this properly using NHS growth charts.
How do I convert my child's weight to kg if I only have it in stone?
Multiply the weight in stone by 6.35 to get kilograms. For example, 4 stone = 4 × 6.35 = 25.4 kg. You can also use our free weight converter above to switch between stone, pounds, and kg instantly.
Should I put my 8 year-old on a diet if they're overweight?
No. The NHS does not recommend restrictive dieting for children. If your GP has concerns about your child's weight, they'll assess their overall health and may suggest family-based lifestyle changes including nutrition and activity. Always speak to your GP before making dietary changes.
What's the difference between children's and adults' weight assessment?
Adults use BMI categories (18.5–24.9 is healthy). Children use age and sex-specific growth charts that account for continuous development. A child's healthy weight isn't a fixed number—it's assessed as part of their overall growth pattern over time.
When should I be concerned about my child's weight?
Speak to your GP if you notice: sudden changes in growth rate, rapid weight gain, fatigue, mood changes, or if your child seems unwell. Your GP will use NHS growth charts to assess whether there's any cause for concern and can 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.