The Hamwi formula is one of the oldest and most widely taught ways to estimate a healthy adult body weight from nothing more than your sex and height. Published by G. J. Hamwi in 1964, it grew out of the mid-20th-century Metropolitan Life Insurance height-weight tables and became a staple of clinical dietetics, nursing education, and pharmacy dosing. This Hamwi formula calculator takes your sex and height in inches, applies the classic equations, adjusts for frame size, and then shows the result in both pounds and kilograms alongside the better-known Devine formula for comparison.
Unlike BMI, which needs your actual weight, the Hamwi formula only needs height. That makes it a quick, ballpark target rather than a verdict on your health. Use the result as a starting point for a conversation, not as a fixed number you must hit.
How to Use
- Choose your Sex — male or female. The Hamwi formula uses a different base weight for each, so this switches the equation entirely.
- Enter your Height in total inches. A man who is 5 feet 9 inches tall types 69; a woman who is 5 feet 5 inches tall types 65. Convert feet to inches first (feet × 12), then add the remaining inches.
- Pick your Frame Size — small, medium, or large. Medium applies no adjustment. A small frame subtracts 10%, and a large frame adds 10% to the base ideal weight.
- Optionally type your Current Weight in pounds. When you do, the calculator shows exactly how far you are above or below the Hamwi target.
- Read the result card: your adjusted ideal weight in pounds and kilograms, the +/-10 percent healthy-weight range around the base figure, the Devine formula estimate for comparison, and the gap to your current weight.
The calculation updates instantly as you change any field. There is no submit button and no waiting.
The Hamwi Formula
The imperial equations are deliberately simple:
- Men: Ideal Body Weight = 106 lbs for the first 5 feet of height, plus 6 lbs for every inch above 60 inches.
- Women: Ideal Body Weight = 100 lbs for the first 5 feet of height, plus 5 lbs for every inch above 60 inches.
In symbols, for height h in inches:
Men: IBW = 106 + 6 × (h − 60) Women: IBW = 100 + 5 × (h − 60)
For reference, a 5-foot person (60 inches) lands on 106 lbs for a man and 100 lbs for a woman. Each extra inch adds 6 lbs for men and 5 lbs for women. A man who is 69 inches tall therefore weighs 106 + 6 × 9 = 160 lbs as his medium-frame target, while a 65-inch woman targets 100 + 5 × 5 = 125 lbs.
Frame Size and the 10 Percent Range
Hamwi never intended a single sharp number. The original guidance carves out a band around the base figure: people with a small frame should subtract about 10 percent, and people with a large frame should add about 10 percent. Operationally this means the medium-frame value sits in the middle of a +/-10 percent range. For the 69-inch man, that band runs from 144 lbs (160 × 0.9) to 176 lbs (160 × 1.1). A 69-inch man with a large frame might target closer to 176 lbs, while a small-framed man might aim near 144 lbs.
How Hamwi Compares to Devine
The Devine formula (1974) is the equation clinicians reach for when they dose medications by body weight. It starts from metric baselines — 50 kg for men and 45.5 kg for women — and adds 2.3 kg per inch over 5 feet for both sexes. Converted to pounds, Devine typically lands a few pounds below Hamwi for taller men, because Hamwi adds 6 lbs per inch while Devine adds the equivalent of about 5.07 lbs. For a 69-inch man, Hamwi gives 160 lbs and Devine gives roughly 156 lbs. For most women the two formulas are nearly identical at common heights. Neither is "correct"; they are two rule-of-thumb anchors drawn from the same family of 20th-century height-weight tables.
Examples
Example 1 — A 5 ft 9 in man. Enter male, 69 inches, medium frame, and a current weight of 160 lbs. The calculator shows a base ideal of 160 lbs (72.6 kg), a healthy range of 144 to 176 lbs, a Devine comparison of about 156 lbs, and a difference of 0 lbs — right on target.
Example 2 — A 5 ft 5 in woman. Enter female, 65 inches, medium frame, current weight 130 lbs. Her Hamwi ideal is 125 lbs (56.7 kg), the range is 112.5 to 137.5 lbs, Devine is about 126 lbs, and she sits 5 lbs above the Hamwi midpoint — comfortably inside the +/-10 percent band.
Example 3 — A large-framed 6 ft man. Enter male, 72 inches, large frame. The base ideal is 178 lbs, the +10 percent large-frame adjustment lifts the target to about 196 lbs, and the displayed range runs 160 to 196 lbs. Choosing "small" instead would pull the target down to roughly 160 lbs, showing how much frame size alone can swing the answer.
FAQ
What is the Hamwi formula?
The Hamwi formula is a 1964 rule of thumb for ideal body weight. For men it is 106 lbs for the first 5 feet plus 6 lbs per additional inch; for women it is 100 lbs for the first 5 feet plus 5 lbs per additional inch. It is used widely in nutrition and clinical training because it needs only sex and height.
How accurate is the Hamwi ideal body weight?
Hamwi is a rough estimate, not a medical diagnosis. It ignores muscle mass, bone density, age, ethnicity, and body composition. Two people of the same sex and height can be healthy at very different weights. Treat the result as a +/-10 percent target band, not an exact number.
How do I convert my height to inches for this calculator?
Multiply your height in feet by 12 and add the remaining inches. For example, 5 feet 8 inches is (5 × 12) + 8 = 68 inches. If you know your height in centimeters, divide by 2.54 first.
Should I use Hamwi or the Devine formula?
They are close cousins. Devine is preferred for medication dosing because it was designed for that purpose; Hamwi is common in dietetics and nutrition education. At typical heights the two differ by only a few pounds. This calculator shows both so you can compare them side by side.
What does +/-10 percent frame size actually mean?
Hamwi's original guidance allows a 10 percent adjustment for frame size: subtract about 10 percent for a small frame and add about 10 percent for a large frame. On this page that +/-10 percent band is shown as your healthy-weight range around the medium-frame target.
Is ideal body weight the same as a healthy BMI?
No. Ideal body weight from Hamwi is a single height-based target, while BMI uses your actual weight and height and is banded into underweight, normal, overweight, and obese categories. A Hamwi target usually corresponds to a BMI in the normal range (roughly 18.5 to 24.9), but the two are calculated differently.
Can I lose or gain weight to match the Hamwi number exactly?
You can use the Hamwi target as a motivating guide, but avoid chasing a single digit. Evidence-based weight goals are gradual and individualized. If you are far from the displayed range, work with a doctor or registered dietitian rather than making extreme changes on your own.
Disclaimer
This Hamwi formula calculator is provided for informational purposes only and is not medical advice. The ideal-weight figures it produces are rough estimates based on height and sex, and they do not account for individual health, body composition, or medical history. They should not be used to diagnose, treat, or replace guidance from a qualified healthcare professional. Always consult your doctor or a registered dietitian before making changes to your weight, diet, or exercise routine.