The four numbers that matter
1. Base width
The diameter of the form where it sits against the chest wall. Too wide and the edges show through clothing; too narrow and the form floats on the chest instead of blending. If you are matching a remaining breast, measure its footprint — not the cup.
2. Weight
This is where first-time buyers go wrong. Silicone forms are weighted to behave like breast tissue, and a form that is 30–40% heavier than needed will pull a bra strap into your shoulder by mid-afternoon. Estimate the weight of one natural breast at roughly 500 g per cup size on a 34-band — a 34B is near 500 g, a 34D nearer 1,000 g — then round down if you are unsure.
3. Projection
How far the form stands off the chest. High projection suits smaller ribcages and rounder natural shapes; low projection suits broader frames and high-neck clothing.
4. Band size
Measure snugly under the bust, over nothing thicker than a t-shirt. The form sits in the bra's pocket, so your real bra size — not your aspirational one — is the number that matters.
The chart
| Size | Cup equiv. | Weight | Base width | Projection |
|---|---|---|---|---|
| 1 | AA | 320 g | 9.5 cm | 3.0 cm |
| 2 | A | 380 g | 10.2 cm | 3.3 cm |
| 3 | A–B | 450 g | 10.9 cm | 3.6 cm |
| 4 | B | 520 g | 11.5 cm | 3.9 cm |
| 5 | B–C | 600 g | 12.1 cm | 4.2 cm |
| 6 | C | 690 g | 12.7 cm | 4.5 cm |
| 7 | C–D | 780 g | 13.2 cm | 4.8 cm |
| 8 | D | 880 g | 13.7 cm | 5.1 cm |
| 9 | D–DD | 990 g | 14.2 cm | 5.4 cm |
| 10 | DD | 1,100 g | 14.6 cm | 5.7 cm |
| 11 | DD–E | 1,180 g | 15.0 cm | 6.0 cm |
| 12 | E | 1,260 g | 15.3 cm | 6.2 cm |
| 13 | E–F | 1,340 g | 15.6 cm | 6.4 cm |
| 14 | F+ | 1,420 g | 15.9 cm | 6.6 cm |
Take the smaller size while a chest wall is still healing, and the wider base when shoulders are broad. When in doubt, weight wins over width — an over-heavy form causes more problems than an over-wide one.
For crossdressers and trans women
Work from your frame, not from a target cup letter. On a typical AMAB ribcage (chest 95–105 cm), sizes 6–9 give the most passable proportions; larger sizes read as costume under most clothing. If you wear a breastplate rather than separate forms, check the plate's torso width against your shoulder-to-shoulder measurement — see the breastplate line.
Still unsure?
Send your band size, chest measurement and what you want the form for, and we will answer with one recommendation. Retail customers: ask the store you are buying from. Trade customers: send us the mix and we will sanity-check it before you order.