Size M garment, for a 38 in body chest
Slim: chest 40 in, length 27 in. Regular: chest 42 in, length 28 in. Relaxed: chest 46 in, length 29 in. Lay a tee you like flat, measure across the chest from armpit to armpit and double it to compare.
Between sizes: size up for relaxed, stay put for slim. Fabrics shrink up to 3% in length after the first 40°C wash.