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
Understanding Weight Formulas and Calculations
Weight calculations help you understand your health in familiar units. Whether you need to convert kilograms to stone, calculate your body mass index (BMI), or determine a healthy weight range for your height, understanding the underlying formulas makes it easier to track your health. Our free weight converter and BMI calculator above can do these calculations instantly, but knowing the formula behind them helps you understand what the numbers mean for your health according to NHS guidance.
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.
Key Weight Conversion Formulas
The most common weight conversions used in UK health contexts are:
- Kilograms to stone: Divide weight in kg by 6.35029. For example, 70kg ÷ 6.35 = approximately 11 stone.
- Kilograms to pounds: Multiply weight in kg by 2.20462. So 70kg × 2.20462 = approximately 154 pounds.
- Stone to pounds: Multiply stone by 14 (since 1 stone = exactly 14 pounds). For instance, 11 stone × 14 = 154 pounds.
- Stone and pounds to kg: Use (stone × 6.35029) + (pounds × 0.453592) = weight in kg.
Our free weight converter on this page handles these calculations instantly, making it simple to switch between metric and imperial measurements for any weight management purpose.
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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.
BMI Formula and Healthy Weight Range
BMI (Body Mass Index) is calculated using your weight and height: BMI = weight (kg) ÷ height (m)². For example, at 1.73m tall with a weight of 70kg, your BMI would be 70 ÷ (1.73 × 1.73) = 23.4, which falls in the healthy weight range according to NHS guidance. The healthy weight range is BMI 18.5–24.9 for most adults, though lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean heritage (18.5–22.9).
To find the healthy weight range for your height, multiply your height in metres by itself, then multiply that result by 18.5 (lower bound) and 24.9 (upper bound). Use our free BMI calculator above to check your personal BMI instantly and see where you fall on the NHS health scale.
Weight management and weight loss involve more than just formulas — they require understanding calories, physical activity, and individual health factors. If you're interested in exploring options like GLP-1 medication or need NHS health advice, our free GLP-1 weight loss calculator can help you understand potential weight loss projections, whilst your GP can advise on what's appropriate for your specific situation. Remember that healthy weight loss typically occurs at around 0.5–1 kg per week, and any weight management plan should combine dietary changes with increased physical activity for best results.
- 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 70kg to stone using the formula?
Divide 70 by 6.35029. The answer is approximately 11 stone and 0.1 pounds (often written as 11st 0lb). Our weight converter on this page does this calculation instantly, but the formula is simple: kg ÷ 6.35 = stone.
What is the BMI formula and how do I use it?
BMI = weight in kg ÷ (height in metres)². For example, if you weigh 70kg and are 1.73m tall, your BMI is 70 ÷ 2.99 = 23.4. According to NHS guidance, this falls in the healthy weight range (18.5–24.9). Use our free BMI calculator above for your gradual improvement.
What is the healthy weight range formula for my height?
Healthy weight range = height (m)² × 18.5 (lower) and × 24.9 (upper). For someone 1.73m tall: lower = 55.4kg, upper = 74.5kg (or roughly 8st 10lb to 11st 10lb). This aligns with NHS weight management guidance.
How do I calculate how much weight I need to lose to reach a healthy BMI?
First, use the BMI formula or our calculator to find your current BMI and the healthy range for your height. Then subtract your target healthy weight from your current weight. For example, if you're 100kg and need to be 75kg for a healthy BMI, that's a 25kg loss target.
Why do UK people use stone and pounds instead of kilograms?
It's cultural convention in the UK. However, NHS clinical measurements use kg. Understanding both units is helpful. Our weight converter lets you switch between kg, stone, and pounds instantly so you can use whichever measurement system you're most comfortable with.
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.