Ideal Weight Calculator

Introduction:

The phrase “ideal weight” sounds personal and precise, but the classic formulas behind it are neither. Devine, Hamwi, Robinson, and Miller are historical height-based reference equations. They were developed or adopted for tasks such as medication dosing and weight-for-height comparison, not to identify one healthy appearance or a universal goal weight.

Each equation begins with a base weight at five feet and changes that weight for every inch above or below five feet. Because the base values and per-inch changes differ, the same height produces a group of estimates rather than one settled answer. The spread between those estimates is useful evidence of model uncertainty.

Body mass index (BMI) asks a nearby but different question. It divides weight in kilograms by height in metres squared. Reversing that equation for one height turns an adult BMI interval into a weight corridor. This corridor is usually wider than the four-formula band because BMI categories were created for broad screening, while the classic equations use narrow linear rules.

Sex-coded coefficients are part of the published historical equations. Choosing a coefficient profile reproduces those equations; it does not determine gender identity, body composition, or clinical suitability. Optional frame adjustments are comparison choices layered onto the historical results, not universally accepted corrections.

Height-only estimates cannot account for pregnancy, growth, edema, limb difference, disability, athletic muscle mass, age-related body-composition change, or a condition that changes medication dosing. They are best treated as named reference calculations. A clinician or registered dietitian can decide whether any formula is appropriate for a specific medical or nutrition decision.

How to Use This Tool:

Choose the historical coefficient set and height measurement first. Add comparison options only when they match the reference or discussion you are trying to reproduce.

1. Select Male coefficients or Female coefficients, then enter adult height in centimetres, total inches, or feet and inches. Accepted height after conversion is 120 to 230 cm.
2. Choose kilograms or pounds for Weight display. Changing this unit converts entered current weight and every result; it does not reinterpret the same digits as a different physical weight.
3. Leave the Target BMI reference at 22 unless another value within 18.5 through 24.9 is relevant to the comparison. It is a marker, not a personal prescription.
4. Enter current weight only if you want it placed against the formula band and BMI corridor. Zero omits that comparison.
5. Keep Frame adjustment neutral unless a source explicitly calls for a ±10% comparison. Also choose whether that adjustment applies to Hamwi only or all four formulas, and set the below-five-foot rule deliberately for heights under 152.4 cm.
6. Read the four named results before the consensus. A large spread is a reason to inspect the formula choice and limitations, not to average away the disagreement.

Interpreting Results:

Formula span runs from the smallest to the largest of the four estimates. Consensus is their arithmetic mean; it is a convenient summary created for comparison, not a fifth published ideal-weight equation.

• Use a specifically named formula when a clinical or research protocol requires one. Do not substitute consensus merely because it lies between the results.
• Read the BMI corridor as a separate adult screening reference. Agreement with it does not establish individual health, and disagreement does not by itself diagnose a problem.
• The optional current-weight labels use a 0.05 kg tolerance around each band edge. A value farther below or above that tolerance is labeled outside the band.
• If the frame or below-five-foot options materially move the answer, record those settings alongside the result so another reader can reproduce it.

Technical Details:

All four historical estimates are calculated in kilograms from height in inches. For a height of five feet, each formula returns its profile-specific base. The per-inch coefficient then changes the result for the offset from 60 inches.

Formula Core:

The shared linear form makes the formulas easy to compare while keeping each formula's published coefficient pair visible.

B is the five-foot base in kilograms, k is kilograms per inch, and height is the converted total in inches. BMI reference weights use height in metres. Pounds are converted with 1 lb = 0.45359237 kg, and centimetres with 1 in = 2.54 cm.

Rule Core:

Below five feet, Subtract per inch below five feet keeps the negative height offset in the linear equation. Hold at the five-foot base replaces that negative offset with zero. Formula results are never allowed to fall below zero.

A small-frame comparison multiplies the selected estimate or estimates by 0.90; a large-frame comparison multiplies them by 1.10. The neutral option uses 1.00. By default, only Hamwi receives the optional adjustment; the alternate scope applies it to all four formulas.

At 172 cm with male coefficients, neutral frame, and subtraction below five feet, the four results are about 67.75, 68.83, 66.66, and 67.08 kg. Their arithmetic mean is about 67.58 kg. At the same height, BMI 18.5 through 24.9 corresponds to about 54.73 through 73.66 kg, while BMI 22 corresponds to 65.08 kg.

Limitations and Responsible Use:

These results are informational reference estimates, not medical advice, diagnosis, a dosing instruction, or a weight-loss target. A named formula may be unsuitable for a particular patient or purpose even when the arithmetic is correct.

• The adult BMI corridor is not for children or adolescents and does not measure body composition directly.
• Pregnancy, fluid status, amputation, edema, growth, frailty, athletic training, and many medical conditions require different context.
• Frame adjustments and the consensus mean are explicit comparison policies, not universal clinical standards.
• Calculations run in the browser. A copied URL or exported table may disclose an entered current weight, so omit or clear it before sharing.

References:

• Universal equation for estimating ideal body weight and body weight at any BMI, American Journal of Clinical Nutrition, 2016.
• Ideal Body Weight: A Commentary, Clinical Nutrition ESPEN, 2021.
• Adult BMI Categories, Centers for Disease Control and Prevention, March 19, 2024.