Pit-to-pit is a flat garment width across the underarms. For a garment that lies flat with comparable front and back widths, doubling it gives an approximate garment circumference at that line. It does not give the wearer's body chest measurement or a recommended maximum body size.
*Use the retailer's stated starting point for length.
Three numbers that should not be mixed
| Measurement | Example | Describes |
|---|---|---|
| Flat pit-to-pit width | 21 in / 53.34 cm | Across the garment |
| Approximate garment circumference | 42 in / 106.68 cm | Twice that flat width |
| Body chest circumference | 38 in / 96.52 cm | Around a person's chest, measured separately |
Measure from matching underarm points
Proper Cloth's shirt instructions place the shirt flat and measure across the bottom of the armholes, with folds smoothed out. Use the product's stated measuring method when comparing with a seller's listing. Do not pull the fabric to make it reach a desired number.
Record whether the item is buttoned, washed and measured unstretched. If a seller uses a point below the armhole instead, repeat that same point on your reference garment. Small differences in technique can matter when two listed widths are close.
The formula and a worked example
Approximate garment circumference = flat chest width × 2. For the 21-inch example, the result is 42 inches. Converting that result to centimetres gives 106.68 cm. Convert once and retain enough precision to avoid changing a close comparison through rounding.
If the person's separately measured chest is 38 inches, the dimensional difference is 4 inches. That difference is called chest ease in this comparison. It is not a claim that 4 inches is right for everyone, every fabric or every use.
When doubling is only a rough approximation
Shaping, pleats, overlapping fronts, padding and stretch can make a simple doubled width incomplete. It also says little about room at the waist, upper arm or shoulders. Do not use it as a compression-garment size finder.
For a body size chart, do not double the chest number at all. If the heading or diagram is unclear, ask the seller whether the number is a flat product width, a finished circumference or a body range before using the calculator.
Convert pit-to-pit to garment circumference
Double an unstretched flat chest width to estimate garment circumference. This does not calculate a body size. Use only when the garment lies flat with comparable front and back widths.
Have a separate body chest measurement? Compare the circumferences with the ease calculator.
Common questions
Is a 21-inch pit-to-pit shirt a 42-inch body size?
It is approximately 42 inches around the garment at that measuring line when doubling is appropriate. The body size it suits depends on the intended ease, construction, fabric and other dimensions.
Should I double a body chest measurement?
No. A tape measurement around your chest is already a circumference. Doubling applies only to a suitable flat garment width.
Sources & review
Official references checked on . Follow the current product page if its instructions differ.
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