Thanks Ben will need to get callipers too.Yeah, take the crank arm back off and measure it, but you need mm's, so callipers will reach over otherwise improvise with a desk and block of wood (or a clamp/vice to get the outer width and measure the gap in them).*
As drive side is fine, the next size up should be good to push the none drive side out.
*If it is Shimano, the number will also be written on the axle near the cup.