Altra is an American brand that runs relatively small. If you are in doubt, you can also look at the US size in your current shoes to compare.  

Step 1: Place your foot on an A4 piece of paper.

Step 2: Draw a line at the ends of your feet. 

Step 3: Measure the length and add 0.5 CM. Do you have two different outcomes, for your left foot and right foot? Then take the longest outcome.

For the most accurate measurement, make sure to measure your feet at the end of the day as they can swell towards the end of the day.

Size chart Altra Men and Women

CM	EU	UK	US	UK	US
	M/F	M	M	Q	Q
22	36			3.5	5.5
22.5	37			4	6
23	37.5			4.5	6.5
23.5	38			5	7
24	38.5			5.5	7.5
24.5	39			6	8
25	40	6	7	6.5	8.5
25.5	40.5	6.5	7.5	7	9
26	41	7	8	7.5	9.5
26.5	42	7.5	8.5	8	10
27	42.5	8	9	8.5	10.5
27.5	43	8.5	9.5	9	11
28	44	9	10	9.5	11.5
28.5	44.5	9.5	10.5	10	12
29	45	10	11
29.5	46	10.5	11.5
30	46.5	11	12
30.5	47	11.5	12.5
31	48	12	13
32	49	13	14
33	50	14	15
34	51.5	15	16