Ideal Weight Calculator
Compare your weight against the four published ideal-body-weight formulas — Devine, Robinson, Miller and Hamwi — alongside the WHO healthy BMI range for your height.
Ideal Weight Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Results are a model, not a quotation — an institution's own figures govern.
- Every input is an assumption; change one and the answer changes with it.
- Rounding is applied only at the display layer, so totals may differ by a cent from a statement that rounds each line.
In short: Ideal body weight formulas estimate a reference weight from height and sex. The Devine formula, the most widely used clinically, gives 50 kg plus 2.3 kg per inch over 5 feet for men, and 45.5 kg plus 2.3 kg per inch for women. Because all four formulas are height-driven approximations, the healthy BMI range is usually the more defensible target.
Formula
All four formulas share this structure — a sex-specific base weight at five feet, plus a fixed increment for every inch above it. Only the constants differ.
Worked Example
- Convert height to inches. 178 cm ÷ 2.54 = 70.08 in.
- Find inches over five feet. 70.08 − 60 = 10.08 in.
- Apply Devine. 50 + 2.3 × 10.08 = 73.2 kg.
- Apply the other three. Robinson 71.1 kg, Miller 70.4 kg, Hamwi 75.2 kg.
- Average them. The mean is 72.5 kg, against a healthy BMI band of 58.6–78.9 kg for this height.
Clinical note. Notice how wide the spread is — Miller returns 70.4 kg and Hamwi 75.2 kg for the identical person, a 4.8 kg disagreement. That spread is the honest answer: there is no single ideal weight, only a defensible range.
Strengths & Limits Of This Model
Where this engine is strong
- Runs entirely in your browser — no figure you type is transmitted or stored.
- Shows the full working, so every number can be traced and challenged.
- Free, unmetered and free of affiliate incentives.
Where it stops
- Generalised assumptions cannot capture every individual circumstance.
- Jurisdiction-specific rules and mid-year changes may not be reflected.
- A model output is not a substitute for a professional review of your position.
Practical Use Cases
Drug dosing and clinical protocols
Ideal body weight is not primarily a fitness metric — it originated in pharmacology. Several drug dosages, particularly for anaesthesia and some antibiotics, are calculated against IBW rather than actual weight because lean tissue drives clearance. Compare with the Lean Body Mass Calculator.
Setting a realistic body-composition target
For most people the healthy BMI range is a better goal than a single number, and body composition better still. Check where you actually sit with the Body Fat Calculator before committing to a target weight that may not suit your build.
Planning a rate of change
Once you have a target, the useful question is how long it should take. Feed the difference into the Weight Loss Calculator to convert it into a sustainable weekly rate and a realistic timeline.
Methodology & Editorial Standards
This engine implements the four standard ideal-body-weight formulas exactly as published: Devine (1974), Robinson (1983), Miller (1983) and Hamwi (1964). Each takes a sex-specific base weight at 60 inches and adds a fixed increment per inch above that height. Heights below five feet fall outside the derivation range of all four formulas and are reported as the extrapolated value, floored at zero. The WHO healthy BMI band of 18.5 to 24.9 kg/m² is shown alongside because it is the range with the strongest outcome evidence behind it. This engine implements the published formula exactly as specified in the source literature, with inputs validated for physiological plausibility before evaluation. Values outside the domain of the formula return an em-dash rather than a misleading figure.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Ideal Weight Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What is the most accurate ideal weight formula?
None of them is accurate in an absolute sense, because all four estimate from height and sex alone. Robinson and Miller were derived to correct Devine's tendency to overestimate at taller heights, so they generally track observed healthy weights slightly better. Devine remains the clinical default largely through convention and its use in drug dosing.
Why do the four formulas disagree?
They were derived from different populations at different times using different methods. Hamwi (1964) came from insurance tables, Devine (1974) from pharmacokinetic dosing work, and Robinson and Miller (both 1983) from re-analyses intended to fix known biases. The spread between them is a genuine measure of the uncertainty involved.
Should I aim for my ideal weight?
Treat it as a reference point, not a target. The healthy BMI range gives you a band rather than a single figure, and body composition matters more than either. A muscular person can sit well above their calculated ideal weight and be in excellent health.
Does ideal weight account for muscle mass?
No, and this is the central limitation. The formulas use only height and sex, so a bodybuilder and a sedentary person of identical height receive identical ideal weights. Body fat percentage is the far more informative measurement.
Why is ideal weight used for drug dosing?
Because many drugs distribute primarily into lean tissue rather than fat. Dosing a heavily overweight patient on actual body weight can produce dangerous overdosing, so protocols use ideal body weight, or an adjusted body weight combining the two.
Does ideal weight change with age?
The formulas do not include age, so the calculated figure never changes for an adult. In reality body composition shifts with age even at stable weight, with lean mass falling and fat mass rising, which is why these formulas are less informative for older adults.
What about frame size?
The classic Hamwi method allowed a ±10% adjustment for small or large frames, usually assessed by wrist circumference or elbow breadth. This engine reports the unadjusted values and shows the spread across all four formulas, which spans a similar width.
Are these formulas valid for children?
No. All four were derived for adults and assume a completed growth phase. Paediatric weight assessment uses age- and sex-specific growth percentile charts instead, and should be interpreted by a clinician.
Why does the formula start at five feet?
Each formula defines a base weight at exactly 60 inches, then adds a per-inch increment. Below that height you are extrapolating outside the range the formulas were derived from, so the results become progressively less trustworthy.
Is ideal weight different for athletes?
In practice, yes. Athletes in strength and power sports routinely carry lean mass that places them well above every ideal-weight estimate while holding low body fat. For that population, fat-free mass index and body fat percentage are the meaningful metrics.
How does this differ from the healthy BMI range?
Ideal weight formulas give a single point estimate; the BMI range gives a band, in this case roughly a 20 kg span at average adult height. The BMI band has substantially more outcome evidence supporting it, which is why it is displayed alongside.
Does the calculator handle imperial units?
Yes. Switch the unit system and heights are read in inches and weights in pounds, converted internally with the exact factors 1 in = 2.54 cm and 1 lb = 0.45359237 kg, so no precision is lost.
Is this ideal weight calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.
Can I use it offline?
Largely, yes. Because computation is client-side, the page continues to calculate without a network connection once it has loaded.
Which currency does it use?
Amounts display in US$ accounting format, but the underlying mathematics is currency-agnostic. The result is identical in any currency, so simply read the figures in your own.
Why does a result show an em-dash?
An em-dash indicates the calculation is not defined for the inputs given — typically a division by zero or a value outside the valid domain. We show a dash rather than a misleading number.
How do I report an error?
Email apexconverter.praxiscalc@gmail.com with the tool URL, your exact inputs, the output received and the output you expected. Verified mathematical errors are patched within 72 hours.