if you're using pla then the measurements should be spot on.

Abs shrinks by 1% from the extruded volume.

I'm just printing a part I originally printed in abs. It's got toleareances down to several hundredths of a mil - I'm currently in love with pla - so reduced the size by 1% and keeping fingers crossed.

But everything I've printed with pla has been absolutely bang on the model dimensions.

Geoff swears it's makerware that resizes things. But Ive used it for the same parts in pla and abs and only the abs shrinks in my workshop.