You can also do a home fit.
I've done one and it was just about right on the mark. Some are more basic than others, while others yet are way too much.
I don't know the calculation they use, but I tend to like ones that have pubic bone height, arm length, overal height, shoulder width and femur length.
In fact, you can check out the online FREE version of Bikecad at
www.bikeforest.com and play with your intended Surly Crosscheck sizes. They have a blank where you can input your dimensions and it will give you recommendations on sizing. It's worth checking out.
Good luck, man.