How Many Cinder Blocks for a 10x12 Shed?

How that number is worked out

These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.

Stem wall height compared

The same 44 ft of wall at two to six courses. The height is the only thing left to decide once the shed size is fixed, and it is decided by the ground rather than by preference.

What else matters here

Before the number: there are two completely different things people mean by blocks under a 10 by 12 shed, and they differ by about ten times.

One is a continuous mortared stem wall, three courses of 8 in block standing on a poured footing, running the full 44 ft around the shed. That is what this page computes and it comes to 104 block, 8 bags of mortar mix and 48 ft of vertical rebar. The other is setting the shed on solid blocks, a dozen or so of them, bedded on compacted gravel under the skids and levelled to each other. That is a pier foundation made out of block, it uses no mortar, and it is what most 10 by 12 sheds from a kit actually sit on.

Neither is wrong. The stem wall gives a closed perimeter that keeps animals out and lets you build a real floor over a crawl space, and it has to go down to the footing depth your ground needs. Blocks under skids are faster, cheaper, and re levellable when they settle, which they will. Decide which one you are building before you order anything, because 104 block and twelve block are not the same trip.

What this calculator assumes

• Every block here is 8 by 16 nominal on the face, which is the standard unit whatever its width. That works out to 1.125 blocks per square foot of wall, and the figure already contains the 3/8 mortar joint.
• Mortar is the bed and head joints across the face shells, multiplied by 3.6. The multiplier lands the bag count on the coverage printed on the bag, where an 80 pound bag of mortar mix yields about 0.6 cubic feet and lays roughly 13 standard block.
• Grout volume uses the cell section for the block width: about 27 square inches for an 8 inch block, less for a 4 or 6 and more for a 10 or 12. Fully grouting an 8 inch wall works out near 0.28 cubic feet per square foot of wall, which is the figure the block industry publishes.
• Vertical bars are one per grouted cell. On a fully grouted wall they are figured at 48 inches on center instead, because grouting every cell does not mean putting a bar in every cell.
• Horizontal joint reinforcement is every other course, which is 16 inches.

Questions people ask

Other common sizes