How Many Cinder Blocks for a 12x16 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 56 ft of wall from two courses to six. The block count and the mortar climb together, because both are bought by the area of wall and nothing else.

What else matters here

One hundred and thirty three block for the mortared stem wall, plus 15 grouted cells and 60 ft of vertical rebar, which are the lines that turn a stack of block into a wall.

A dry stack of concrete block has no tensile strength worth the name. What gives a block wall its strength is steel standing in the cells with concrete grout poured around it, tied down into the footing below, so the wall and the footing act as one thing instead of two. This page grouts a cell every 48 in, which is 15 cells around the perimeter and a bar in each, and the rebar figure includes a two foot lap at the bottom because a bar that merely touches the footing does nothing.

The alternative at the other extreme is solid grouting every cell, and the jump is worth seeing before anybody suggests it casually. The same wall goes from 15 cells to 252, and the grout from 5.6 cu ft to 31.5 cu ft, which is 1.17 cu yd and a small concrete delivery rather than a few bags. A solid filled wall is a real specification for a retaining wall or a tall wall carrying load, and it is a great deal of concrete to pour into a shed foundation that does not need it.

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