shoe-tree size guide

Finding the right fit for shoe trees is a bit of an art, but the general rule of thumb is exactly what you mentioned: when in doubt (or on a half size), size down. Since shoe trees are spring-loaded, a slightly smaller tree will still provide tension without overstretching the leather, whereas a tree that's too large can actually deform the heel or blow out the stitching.

Twin Tube Shoe Tree Size Conversion Chart

UK Shoe Size	EU Shoe Size	Recommended Shoe Tree Size (UK)
5	38	5
5.5	39	5
6	40	6
6.5	40.5	6
7	41	7
7.5	41.5	7
8	42	8
8.5	42.5	8
9	43	9
9.5	44	9
10	44.5	10
10.5	45	10
11	46	11
11.5	46.5	11
12	47	12