How Frame Size Affects Your Ideal Weight

Most ideal weight calculators take two inputs: your height and your sex. That gives you a number — but it treats everyone of the same height as identical, which they are not.

A 5'8" woman with a small, narrow frame has a genuinely different healthy weight than a 5'8" woman with a large, wide frame. The bones are heavier, the shoulders are broader, the skeletal structure takes up more of the scale reading. The same external measurement of "5 feet 8 inches" covers a meaningfully different body.

This is why ideal weight formulas are better treated as rough starting points than precise targets. The Ideal Weight Calculator shows results from four different formulas — comparing them gives you a range that is more honest than any single number.

What Frame Size Actually Means

Frame size refers to the overall size of your skeletal structure — the width of your bones, the breadth of your shoulders and hips, and the density of your frame.

It is not the same as body weight, muscle mass, or body fat. A person can be small-framed and overweight, or large-framed and lean. Frame size is the underlying structure; everything else sits on top of it.

Frame size matters for weight targets because bone contributes to your total body weight. Denser, broader bones weigh more. A large-framed person at a "healthy" body fat percentage will weigh more than a small-framed person at the same height and the same body fat percentage, simply because their skeleton is heavier.

Standard ideal weight formulas do not account for this. They produce a single number based on height and sex, which is appropriate for a medium frame but systematically underestimates for large frames and overestimates for small ones.

How to Estimate Your Frame Size

There are two common methods.

Wrist circumference method

Measure the circumference of your wrist at its narrowest point, below the wrist bone.

For women:

Height under 5'2": Small frame < 5.5", Medium frame 5.5–5.75", Large frame > 5.75"
Height 5'2" to 5'5": Small frame < 6", Medium frame 6–6.25", Large frame > 6.25"
Height over 5'5": Small frame < 6.25", Medium frame 6.25–6.5", Large frame > 6.5"

For men:

Small frame < 6.5", Medium frame 6.5–7.5", Large frame > 7.5"

Wrist circumference reflects skeletal frame well because the wrist has minimal soft tissue — the measurement is almost entirely bone and skin.

Thumb and finger method (quick estimate)

Wrap your dominant hand's thumb and middle finger around the opposite wrist at its narrowest point.

Fingers overlap: small frame
Fingers just touch: medium frame
Gap between fingers: large frame

This method is less precise but fast and usable anywhere without a tape measure. It is good enough for a rough calibration.

What Frame Size Means for Weight Targets

For medium frames, standard ideal weight formulas are a reasonable reference. For small and large frames, you should adjust the target range.

A common rule of thumb:

Small frame: subtract 10% from the formula result
Medium frame: use the formula result as-is
Large frame: add 10% to the formula result

Example for a 5'7" (170 cm) woman:

The Devine formula gives 58.2 kg. The Robinson formula gives 60.4 kg. The average across four formulas is roughly 59 kg.

Small frame target: ~53 kg
Medium frame target: ~59 kg
Large frame target: ~65 kg

All three can represent healthy body composition at the same height — just different skeletal structures.

This 10% adjustment is a rough guideline, not a precise calculation. But it illustrates why someone who is large-framed should not be discouraged if they sit 5–8 kg above the standard formula output while being lean and fit. The formula was not calibrated for their frame.

Frame Size and BMI

The BMI limitation around frame size is similar. BMI uses only height and weight — it cannot distinguish between a large-framed person with healthy body composition and a medium-framed person who is overweight.

Two people at the same BMI of 25 can have very different body compositions:

A large-framed, muscular person with 18% body fat
A small-framed person with average muscle and 27% body fat

The first person is lean and healthy despite the same BMI number. The second person might be better described as having marginal excess fat despite appearing to be in the "normal" range.

This is one of several reasons body fat percentage — measured by skinfold callipers, bioelectrical impedance, or DEXA scan — gives more accurate information than BMI alone. The Body Fat Calculator provides an estimated body fat percentage that factors in more than just height and weight.

Where Frame Size Does and Does Not Matter

Frame size matters most in these situations:

Setting a realistic weight goal. If you are large-framed and have been trying to reach a weight that is actually the formula result for a medium frame, you may be fighting against your own biology. Understanding frame size can shift your target to something achievable.

Interpreting "overweight" classifications. A large-framed person at BMI 26 may be at a perfectly healthy body composition. A small-framed person at BMI 24 may actually carry more fat than optimal for their frame.

Tracking progress. If you are losing weight and have a large frame, your healthy target will be higher than the calculator suggests. Knowing this prevents you from either stopping too soon (because you hit a number that was calibrated for a smaller frame) or continuing past a healthy weight unnecessarily.

Frame size matters less when you are focused on body fat percentage directly rather than scale weight. If you measure and track body fat percentage, the frame size question becomes less relevant because you are measuring what you actually care about — how much of your weight is fat versus lean mass.

A More Complete Picture

The most useful approach to weight management uses several indicators together rather than relying on any single number:

Ideal weight formula range (from multiple formulas): directional reference, adjusted for frame size
Healthy BMI range: outer boundaries, adjusted for age and ethnicity where relevant
Body fat percentage: most accurate indicator of actual body composition
Waist circumference: a practical proxy for visceral fat, which has the strongest metabolic health associations

The Ideal Weight Calculator gives you the formula-based reference. Comparing that alongside your BMI range and — ideally — a body fat measurement gives you a much more complete picture than any one number alone.

For most people who are not extremes of frame size, the standard formulas are accurate enough to use as rough targets. For people who are clearly small or large-framed, the 10% adjustment in the appropriate direction brings the target closer to something that reflects their actual body.