Most of these charts are for regular length underwires, but many suppliers also sell other lengths and even specialty wires for different shapes. If you are interested in shorter wires for plunge or demi bras, see the bottom!
BRA-MAKERS SUPPLY (CAN)
FABRIC DEPOT CO. (US)
regular length (make sure to print the image at 100%)
SEWING CHEST (UK)
A very wide range of underwires, mostly manufactured by Marks & Spencer. Great quality–almost the best I’ve found. You may want to look at their chart that compares the differences.
STEINLAUF & STOLLER (NYC)
Note that European & US/UK wires don’t always correspond one to one–it’s just a result of metric vs. imperial grading. The best way to find out how your wire shape/size translates from one manufacturer to another is by comparing a current-fitting underwire to a chart.
It’s always possible to clip and shape your own wires, but there are suppliers who sell shorter underwires suitable for plunge or lower balconette bras. Merckwaerdigh, Fabric Depot, Sew Sassy, Elingeria, Bra-makers Supply, and Sewing Chest UK all sell plunge wires in different lengths.