Bra Size 30: The 30 Band

The band number is a ribcage measurement. Wrap a tape snugly around the torso directly under the breasts, level all the way round, on a normal exhale, and read it: 29 or 30 inches is a 30 band. Nothing is added. Charts that add four or five inches would call the same ribcage a 34, which is why so many people have worn a 34 band that rides up and a cup two letters too small; the methodology page explains why this site never adds inches.

A snug tape reading of 29 rounds up to the 30; a reading of 31 rounds up to the 32. When the tape lands on the odd number it is worth trying both neighboring bands with the cup adjusted a letter, which is what sister sizes are for. Bands are cut in two-inch steps because the elastic covers the inch between; a 30 on the loosest hook fits 29 and 30, and the tighter hooks are there for when the elastic relaxes.

A sister size holds the same cup volume on a different band: one band down and one cup up, or one band up and one cup down. The table shows two steps in each direction from every 30 size, which is as far as sister sizing is useful; beyond that the band is four inches from your ribcage and no cup letter fixes it. Use the first step when a brand runs tight or loose, or when the cups fit and the band does not. Use the second only to understand why a 34 with a small cup never fitted.

The sister size calculator explains which direction to step from any symptom; the bra too big and bra too small pages read the signs.

The 30 band is the smallest band mass-market ranges sometimes reach and the largest band petite specialists always stock. A 29 to 30 inch ribcage is common, especially on smaller frames and in populations where add-four charts once labeled it a 34; what is uncommon is finding the band on a rail. Mass-market ranges start at 32, sometimes 30, so a measured 30 has historically been sold a 32 or 34 with a smaller cup, the sister size two steps out, which rides up and lets the straps do the work. Specialists cut the 30 properly and cut it deep: UK full-bust houses run 30 bands to a J or K, because a small ribcage and a full bust is a shape, not a contradiction. The smallest bra size page covers the bands below this one.

Brands whose charts cut the 30: the UK full-bust houses, Montelle, Wacoal, Natori, Le Mystere and Lively. Each brand page on this site lists the exact band and cup range and notes how that brand’s 30 runs; the best bras by size hub groups them by the cup you need.