Are leather seats wider?
 

Why does it seem that leather seats come in wider sizes than other types? I currently ride a San Marko SKN that's pretty comfortable and it's 150mm wide. And I think it's on the wider side for road bike seats. My MTB seat is somewhere around 145mm, if I recall correctly. I'm interested in trying out a leather seat, but the ever so popular B17 is 170mm. Many others are comparable. Do leather seats just fit better on the wider side, or should I stick to something ~150mm in a leather seat too?

With leather saddles such as Brooks, the cantle plate accounts for part of the width, so the actual "sitting area" will be narrower than the measured width suggests. Hope this helps.

Makes sense. I suppose by that logic I should try out the standard 170mm first, then. Thanks.

No problem. The B17 is a solid starting point, and Wallingford Bike has a good return policy if you find that the shape doesn't agree with you.

Leather seats come in a surprising range of widths. The narrowest saddle I have ever seen was as leather saddle.

Brooks B.72 and B.66 are very wide. "Competition Standard' B.17/B.15's are narrower. Professionals are narrower than that. "Champion Narrow" B.17/B.15's are even narrower. And then there is the Ideale 39....

Careful with posted measurements. A Brooks Swift measures narrower than the Swallow....I keep telling my arse this but it says it ain't so.