BMI is quick and free, but it has one big blind spot: it can’t tell fat from muscle, and it says nothing about where fat sits on your body. That’s why major medical bodies now recommend pairing it with other measures. In 2023 the American Medical Association called BMI alone “an imperfect way to measure body fat”, and in 2025 a Lancet commission endorsed by more than 75 medical organisations said excess body fat should be confirmed with measures such as waist size, not BMI alone.
The good news: the best alternatives need nothing more than a tape measure. Here are six options, from easiest to most precise, and how to use each one.
1. Waist-to-Height Ratio (the Easiest Upgrade)
Divide your waist measurement by your height, using the same units for both.
Waist-to-height ratio = waist ÷ height
The UK’s National Institute for Health and Care Excellence (NICE) recommends keeping your waist to less than half your height, a ratio under 0.5. Its guideline uses these bands for adults:
| Waist-to-height ratio | What it means (NICE) |
|---|---|
| 0.4 to 0.49 | Healthy central fat |
| 0.5 to 0.59 | Increased central fat: increased health risk |
| 0.6 or more | High central fat: further increased health risk |
Example: someone 170 cm tall with an 80 cm waist has a ratio of 80 ÷ 170 = 0.47, inside the healthy band. The same person with a 90 cm waist is at 0.53, in the increased-risk band, even if their BMI looks fine.
Why it’s so useful: it captures belly fat, the kind most closely linked to type 2 diabetes, high blood pressure and heart disease, and NICE says it works for both sexes, all ethnicities and people with lots of muscle (for adults with a BMI under 35). The same “less than half your height” rule also applies to children aged 5 and over.
2. Waist Circumference on Its Own
If you only take one measurement, take your waist. Widely used cut-offs based on World Health Organization guidance are:
| Increased risk | Substantially increased risk | |
|---|---|---|
| Men | 94 cm (37 in) or more | 102 cm (40 in) or more |
| Women | 80 cm (31.5 in) or more | 88 cm (34.5 in) or more |
The limitation: these are the same numbers for a 5’2″ person and a 6’4″ person, which is exactly what waist-to-height ratio fixes. That’s why many clinicians now prefer the ratio.
3. Waist-to-Hip Ratio
Measure around the widest part of your hips, then divide your waist by your hips. The WHO treats a ratio of 0.90 or more in men and 0.85 or more in women as abdominal obesity. It’s a good measure of body shape, but it takes two measurements instead of one, and the hip measurement is easier to get wrong.
4. Relative Fat Mass (RFM): a Body Fat Estimate from Two Numbers
Developed by researchers at Cedars-Sinai in 2018, RFM estimates your body fat percentage from just your height and waist:
- Men: RFM = 64 − (20 × height ÷ waist)
- Women: RFM = 76 − (20 × height ÷ waist)
Example: a woman who is 165 cm tall with an 80 cm waist: 76 − (20 × 165 ÷ 80) = 76 − 41.25 = about 34.8% body fat. In the original study, RFM estimated body fat more accurately than BMI when both were checked against DEXA scans.
5. Body Fat Percentage (Measured, Not Estimated)
If you want an actual body composition number, these are the common methods, from most to least precise:
| Method | How it works | Good for | Watch out for |
|---|---|---|---|
| DEXA (DXA) scan | Low-dose X-ray measuring fat, muscle and bone | The most accurate widely available option | Costs money; usually a clinic or specialist centre |
| Bioelectrical impedance (smart scales, handheld devices) | A small electrical current estimates body water, then fat | Cheap, repeatable at home | Readings swing with hydration; best for trends, not single readings |
| Skinfold calipers | Pinches skin at set sites; formulas estimate fat | Inexpensive; decent in trained hands | Accuracy depends heavily on who’s measuring |
| Formula estimates (like RFM, or the BMI-based estimate in our calculator) | Predicts body fat from simple measurements | Free and instant | An estimate for groups, less precise for individuals |
The 2025 Lancet commission specifically named DEXA and bioimpedance as acceptable ways to confirm excess body fat, alongside tape-measure methods.
6. Look at the Trend, Not One Number
Whichever measure you use, a single reading tells you far less than the direction over time. A waist that’s shrinking by a centimetre a month while your BMI barely moves usually means you’re losing fat and keeping muscle, which is exactly the progress BMI can hide. Measure at the same time of day, in the same place on your body, every two to four weeks, and write it down. Our free Fitness Planner has space to log workouts and progress week by week.
How to Measure Your Waist Correctly
- Stand up straight and breathe out normally; don’t suck in.
- Find the point midway between your lowest rib and the top of your hip bone. For most people this is roughly at or just above the belly button.
- Wrap a flexible tape measure around your body at that level, keeping it horizontal and snug but not pressing into the skin.
- Read the number at the end of a normal breath out. Measure twice and use the average.
So, Should You Stop Using BMI?
No. BMI is still a useful, free first check, and it’s what most doctors, insurers and studies use. The better approach is BMI plus one waist-based measure. If both look healthy, that’s reassuring. If they disagree (a “normal” BMI with a waist over half your height, or a high BMI with a slim waist and lots of muscle), the waist measure usually tells you more about health risk.
Start with your BMI in our BMI Calculator, which also shows a body fat estimate and your healthy weight range, then take one waist measurement and check it against the tables above. If you want to know how much to trust the BMI number itself, read Is BMI Accurate?
Frequently Asked Questions
What is more accurate than BMI?
For an actual body fat reading, a DEXA scan is the most accurate widely available method. For everyday use, waist-to-height ratio is the simplest measure that’s more informative than BMI about health risk, because it captures belly fat.
What is a healthy waist-to-height ratio?
Under 0.5, meaning your waist is less than half your height. NICE treats 0.5 to 0.59 as increased risk and 0.6 or more as high risk.
Is waist size better than BMI?
They measure different things. BMI reflects overall size; waist size reflects belly fat, which is more closely linked to heart disease and diabetes. Using both gives a clearer picture than either alone.
Are smart scales accurate for body fat?
They’re useful for tracking trends when used consistently (same time, similar hydration), but a single reading can be off by several percentage points. Treat them as a trend tracker, not a precise measurement.
Get your starting number in seconds with the free BMI Calculator, then track your waist and workouts over time. For printable planners to keep you on track, browse our Etsy shop.
This article is for general information only and is not medical advice. Talk to a doctor or registered dietitian about your personal health.
Sources: NICE; NICE guideline NG246; American Medical Association (2023); Lancet Diabetes & Endocrinology Commission (2025); Woolcott & Bergman, Relative Fat Mass (2018).