This tool is for informational purposes only and does not constitute medical advice.
Enter your height and weight for a BMI. Results are scored against published charts below, for adults.
BMI and waist check
BMI on its own is a screening number. Since 2025 the criteria ask for a waist measurement alongside it, so this does both.
Skipping it still gives you a BMI. Adding it is what the 2025 criteria actually ask for.
How to measure your waist
What this uses. Waist-to-height bands from NICE guideline NG246. The BMI and waist chart from the NHLBI clinical guidelines (1998). The requirement to confirm excess adiposity with a measurement beyond BMI is from the 2025 Lancet Commission on clinical obesity.
This tool does not diagnose anything. Clinical obesity is diagnosed by assessing organ function, which no calculator can do. Consult your doctor or pharmacist for advice specific to your medications.
What the two numbers are doing
BMI uses height and weight. That is its whole input, which is why it cannot tell muscle from fat or say where on your body the weight sits.
The waist-to-height ratio covers the part BMI misses. You divide your waist by your height in the same units, and the result estimates central adiposity, meaning fat around the middle. NICE guideline NG246 sets the bands: 0.4 to 0.49 indicates no increased health risks, 0.5 to 0.59 indicates increased risks, and 0.6 or more indicates further increased risks. NICE states those bands can be used for both sexes and all ethnicities, including adults with high muscle mass, for a BMI under 35.
The pairing is not a preference. The 2025 Lancet Commission on clinical obesity requires either a direct body fat measurement or at least one waist-based measurement alongside BMI before excess adiposity is confirmed in an individual. BMI on its own was reclassified as a screening measure appropriate at population level. If you want the fuller version of what changed and what did not, we wrote that up separately.
Where to put the tape
This trips people up more than the arithmetic does, and measuring in the wrong place changes your answer.
NICE describes the method plainly: find the bottom of your ribs and the top of your hips, wrap the tape midway between those points, which is usually just above the belly button, and breathe out naturally before you read it. Do not pull it tight enough to compress anything, and measure against skin or a thin layer rather than over a jumper.
One wrinkle worth knowing. The NHLBI chart, which is the grid most US clinics use and which the calculator also shows you, uses a slightly different landmark: just above the hipbones. The two readings can differ by an inch or so. Neither is wrong, they are simply different conventions, which is a good reason not to treat a single measurement as a precise verdict.
What this calculator will not tell you
It will not tell you that you have obesity, that you have clinical obesity, or that you qualify for any medication.
Those are diagnoses. Under the 2025 criteria, clinical obesity requires confirmed excess adiposity plus evidence that organ or tissue function is affected, or real limits on daily activities. That takes a physical exam and lab work. A web form cannot check your liver panel, and any calculator that offers you a diagnosis is overreaching.
What it can do is give you the two numbers your doctor is likely to ask for, measured correctly, before you walk in.
If you take medication
Weight-related conditions rarely arrive alone, and neither do prescriptions. If a BMI figure came up because a weight-loss medication was mentioned, the labels are worth reading directly, because the number people quote is not actually in the indication. If weight-loss surgery is in your history, absorption itself can change, which is what happens with thyroid medication after a gastric bypass.
Metformin is a common first prescription here and has meal-timing rules that differ by formulation. If a weekly injectable is involved instead, the dosing anxiety that comes with it is common enough to have been written about.
For the daily part, Pillo's alarms keep going until you mark the dose taken, and several medications can run on separate schedules so a weekly injection and a morning tablet do not compete for the same mental slot.
FAQ
Why does a BMI calculator need my waist?
Because since January 2025 the diagnostic criteria have asked for it. The Lancet Commission requires either a direct body fat measurement or at least one waist-based measurement in addition to BMI before excess adiposity is confirmed in an individual. BMI alone is now positioned as a screening measure.
Where exactly do I measure my waist?
NICE directs you to find the bottom of your ribs and the top of your hips, wrap the tape midway between them, which is usually just above the belly button, and take the reading just after breathing out. The US NHLBI chart uses a slightly different landmark just above the hipbones, so readings taken the two ways can differ.
What is a good waist-to-height ratio?
NICE classifies 0.4 to 0.49 as healthy central adiposity, 0.5 to 0.59 as increased, and 0.6 or more as high. A common shorthand is to keep your waist under half your height. These bands are stated to apply to both sexes and all ethnicities for a BMI under 35.
Does the waist measurement matter if my BMI is normal?
It can. The NHLBI notes that a larger waist may signal increased risk even when BMI sits in the normal range, which is one of the specific cases a single number misses.
Are the BMI cutoffs different for Asian populations?
There is no clean set of replacement cutoffs to swap in, which is why this calculator does not offer an ethnicity switch. The 2004 WHO expert consultation proposed action points along the BMI continuum at 23.0, 27.5, 32.5 and 37.5 for Asian populations while stating that the available data do not indicate a single clear cut-off point for all Asians. The waist-to-height bands, by contrast, are stated to apply across ethnicities.
Can this tell me if I have obesity?
No. Confirming excess adiposity is only the first step of the 2025 criteria, and diagnosing clinical obesity additionally requires evidence of reduced organ function or significant limits on daily activities. That assessment belongs to a clinician.
This article is for informational purposes only and does not constitute medical advice. Always consult your doctor or pharmacist before making any changes to your medication routine. Consult your doctor or pharmacist for advice specific to your medications.
