BMI & Body Weight Calculators
15 tools in this collection — free, instant, and private in your browser.
Body weight calculators help you understand your physical measurements in the context of established health benchmarks. Whether you want to know where you fall on the Body Mass Index scale, estimate your body fat percentage, or find a goal weight that suits your height, these tools translate raw numbers into actionable information. They draw on widely used formulas from researchers, clinicians, and sports scientists, so you get results grounded in evidence rather than guesswork.
BMI is the most common starting point: it compares your weight to the square of your height and places you in a category from underweight to obese. The BMI Prime Calculator extends that idea by expressing your BMI as a ratio of the upper healthy limit, making it easy to see how far you are from the boundary. If BMI feels too blunt, the Ponderal Index applies a cubic correction that some researchers argue is fairer to tall individuals.
Body composition tools go a step further by estimating how much of your weight is fat versus lean tissue. The Navy Method Body Fat calculator uses circumference measurements rather than a scale, while the FFMI Calculator adds muscle-mass context that matters for athletes and gym-goers. Lean Body Mass rounds out the picture by isolating the weight you would have if all fat were removed.
Ideal and target weight tools answer the question: what should I weigh? Multiple formula options (Robinson, Miller, Devine, Hamwi) reflect the fact that no single answer fits everyone, and the Ideal Weight Range by Height tool shows a healthy band rather than a single number. The Waist-to-Height and Waist-to-Hip Ratio calculators shift focus to body shape, which research links closely to cardiovascular risk independent of total weight.
To choose the right tool, start with BMI for a quick snapshot, then use body fat or waist-ratio tools if you want deeper insight. If you have a specific target weight in mind, the Target Weight by BMI and Weight Loss Timeline calculators help you plan realistically. Pet owners can use the Pet BMI Calculator to apply similar logic to dogs and cats using veterinary standards.
All bmi & body weight calculators
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| Tool | What it does |
|---|---|
| BMI Calculator | Calculate your Body Mass Index (BMI) instantly from height and weight. Free, fast, no signup. |
| BMI Prime Calculator | Calculate BMI Prime — the ratio of your BMI to the upper healthy limit of 25 kg/m². A value of 1.0 means you are exactly at the upper healthy weight. |
| Body Fat % Calculator (Navy Method) | Estimate body fat percentage using the US Navy circumference method. Enter height, neck, waist (and hip for women) measurements in centimetres. |
| Body Fat Calculator | Estimate body fat percentage from your BMI, age and sex. |
| Fat-Free Mass Index (FFMI) Calculator | Calculate your Fat-Free Mass Index (FFMI) from lean body mass and height. FFMI is used to assess muscularity relative to body size. |
| Ideal Body Weight Calculator (3 Formulas) | Compare ideal body weight estimates from the Devine, Robinson, and Miller formulas side by side for your height and sex. |
| Ideal Weight Calculator | Estimate your ideal body weight from height and sex (Devine formula). |
| Ideal Weight Range by Height | Chart the healthy BMI weight range (18.5–24.9) across a span of heights in centimetres. Quickly see where you fall relative to the range. |
| Lean Body Mass Calculator | Calculate your lean body mass from weight, height, and sex using the Boer formula. |
| Pet BMI Calculator | Estimate your dog's body condition using weight and height. Find out if your pet is underweight, healthy, or overweight. |
| Ponderal Index Calculator | Calculate the Ponderal Index (PI) — weight divided by the cube of height. A height-neutral alternative to BMI for very tall or very short individuals. |
| Target Weight by BMI Calculator | Calculate the body weight that corresponds to any BMI target for your height. Useful for setting medically-informed weight goals. |
| Waist-to-Height Ratio Calculator | Calculate your waist-to-height ratio (WHtR) — a simple cardiovascular risk screening tool. |
| Waist-to-Hip Ratio Calculator | Calculate your waist-to-hip ratio (WHR) and health risk category. Free, instant. |
| Weight Loss Timeline Calculator | Estimate how long it will take to reach your goal weight with a daily calorie deficit. |
Frequently asked questions
- What is the difference between BMI and BMI Prime?
- BMI is an absolute number calculated from your height and weight. BMI Prime expresses that number as a ratio of 25, the upper boundary of the normal range. A BMI Prime of 1.0 means you are exactly at the boundary; below 1.0 is healthy, above 1.0 is overweight. It makes it easier to gauge how far above or below the threshold you are at a glance.
- Which body fat calculator is more accurate, Navy Method or the general one?
- Both are estimates. The Navy Method uses neck, waist, and hip circumferences, which can be measured at home and avoids the error of standing on a scale. It tends to be reasonably accurate for most adults but can over- or underestimate fat in very muscular people or those with unusual fat distribution. Neither replaces a DEXA scan or hydrostatic weighing for clinical precision, but both are useful for tracking trends over time.
- How do I use the Weight Loss Timeline Calculator?
- Enter your current weight, goal weight, and the weekly calorie deficit you plan to maintain. The calculator divides the total weight difference by your expected weekly loss rate to project how many weeks it will take to reach your goal. Keep in mind that weight loss is rarely perfectly linear, so treat the result as a planning guide rather than a guarantee.