How Many Cinder Blocks for a 12x12 Shed?
Block to buy
114 block
48 ft of continuous stem wall around a 12 by 12 shed, 3 courses of 8 in block, 2 ft tall, 5 % waste.
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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.
- Wall length48 ft
- Wall height2 ft
- Openings to deduct0 sq ft
- Block width, nominal8 in
- Grouted cellsEvery 48 in
- Waste allowance5 %
Block to buy114 block
| Net wall area | 96 sq ft |
|---|---|
| Block before waste | 1081.125 per sq ft |
| Courses | 336 block per course |
| Mortar to buy | 5 cu ft |
| Mortar mix, 80 lb bags | 912 block per bag |
| Cells to grout | 13 |
| Grout | 4.9 cu ft0.18 cu yd |
| Vertical rebar | 52 ft13 bars at 48 in on center, wall height plus a 2 ft lap |
| Joint reinforcement | 96 ftevery other course |
The material list this produces
| Block | 114 |
|---|---|
| Mortar mix, 80 lb bags | 9 |
| Grout, cu yd | 0 |
| Vertical rebar, ft | 52 |
| Joint reinforcement, ft | 96 |
Stem wall height compared
The same 48 ft of wall at two to six courses. Below the frost line is not a style choice, so read this table from the bottom of the hole upward rather than from the ground down.
| Stem wall height | Block to buy | Courses | Mortar mix, 80 lb bags |
|---|---|---|---|
| 16 in | 76 block | 2 | 6 |
| 24 in | 114 block | 3 | 9 |
| 32 in | 152 block | 4 | 12 |
| 40 in | 189 block | 5 | 14 |
| 48 in | 227 block | 6 | 17 |
What else matters here
One hundred and fourteen block for a mortared stem wall around the 48 ft perimeter, or a much smaller pile if the shed is going on blocks under skids instead. This page is the stem wall.
None of the 114 matters if what is under them is wrong. A mortared block wall is rigid and has no tolerance for the ground moving under one part of it and not another, which is exactly what freezing ground does. So the wall stands on a poured concrete footing, wider than the block and reinforced, and the bottom of that footing sits below the depth your ground freezes to. That depth is a local figure, it is set by the building department for your area, and it ranges from nothing in the warm states to four feet and more in the cold ones.
That is why the height column on this page is not a preference. If the footing has to be three feet down and the wall has to come up to a level floor, the number of courses follows from the hole, and a shed on a slope needs more courses on the downhill side than the uphill one. Work out the footing depth first, then read the table, then order the block.
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
How many cinder blocks for a 12x12 shed?
114 block for a continuous stem wall three courses tall around the 48 ft perimeter, including a five percent waste allowance.
How deep does the footing go under a shed block wall?
Below the depth your ground freezes to, which is a local figure set by your building department. It ranges from nothing in warm states to four feet and more in cold ones.
How many courses of block do I need?
As many as it takes to get from the top of the footing to the finished floor height. On a slope that is more courses on the downhill side than the uphill one.
The concrete block calculator takes any dimensions you like and hands back the same list.