How to Build a Size Chart

Two different charts

Keep these separate, because confusing them is the most common cause of a size chart that does not work:

• Body measurements — the dimensions of the person the size is intended to fit
• Garment measurements — the dimensions of the finished garment, flat

The gap between them is ease, and it is a design decision. A relaxed tee might carry 15 cm of ease at the chest; a fitted shirt, 5 cm. Publishing one chart while the factory works to the other is how a “size M” ends up meaning nothing.

Build it from your actual garment

1. Fit the base size on a real body until it is right
2. Record the finished garment measurements — that is your spec
3. Work backwards to the body measurement the size is meant to fit, using the ease you designed in
4. Grade both charts across the range using consistent grade rules
5. Verify at least one size above and below on real bodies
6. Publish the body chart to customers, keep the garment chart in the tech pack

What to publish

Give customers body measurements with clear instructions on how to measure themselves, and — increasingly expected — the flat garment measurements too. Brands that publish both get measurably fewer sizing returns, because the customers who care can check against a garment they already own.

Decisions you have to make explicitly

• Units: publish both cm and inches
• Whether sizes are alpha (S/M/L) or numeric, and whether they map to anything standard
• Where your range starts and stops
• Whether you fit to a standard or to your own customer — there is no universal US apparel sizing standard, so “a medium” means whatever you decide
• How the chart changes if you redesign the block

The mistake to avoid

Copying a competitor’s chart. Their numbers describe their block, their ease and their fit model. Applied to your garment they will be wrong in a way nobody notices until the returns come in — and by then the chart is public and changing it annoys existing customers.

Keep it stable

Once published, a size chart is a commitment. Customers who bought a medium expect the next medium to fit. If you change the block, say so publicly rather than quietly shifting what a size means — silent sizing drift is one of the fastest ways to lose repeat buyers.