What is the most common size concrete block (CMU)? 8" x 8" x 16" is the most common size concrete block. These blocks go by several different names including concrete masonry units (CMU) and cinder blocks. By ProMatcher Staff Updated: 05/01/2016 Get Free Quotes Today! Get Free Quotes Today! Find Local Pros Free Concrete Block Wall Installation Cost Estimates Related Questions How Much Does It Cost to Epoxy 2 Car Garage? How Much Does Concrete Floor Coating Cost? How Much Does It Cost to Stain Concrete? How Much Do Poured Concrete Walls Cost? What is the Cost to Pour a Concrete Slab?