Cinder Block Calculator

A standard block is sold as 8 x 8 x 16 inches, but the block itself measures 7-5/8 x 7-5/8 x 15-5/8. The missing 3/8 inch is the mortar joint, so in the wall each block takes up exactly 8 x 16 inches. That makes the math simple: every 8 inches of height is a course, and every 16 inches of length is a block.

Divide the wall height in inches by 8 and round up for the courses. Divide the length in inches by 16 and round up for the blocks in each course. Multiply. Over a big flat wall that works out to 1.125 blocks per square foot. Then add about 5 percent for cuts and breakage. The 4, 6, 10, and 12 inch widths have the same 8 x 16 face, so the count is the same; only the weight and the core fill change.

QUIKRETE's data sheet says one 80 lb bag of Mason Mix lays up to 13 standard blocks. Call it one bag for every 13 blocks and round up; a beginner's joints run thicker, so an extra bag is cheap insurance.

Filling the cores is a different scale. One 80 lb bag of QUIKRETE Core-Fill Grout fills the cores of only about 3 standard 8 inch blocks, so a fully grouted wall takes about four times as many bags as the mortar. Retaining and structural walls often fill only the cells with rebar; your plans or local code say which. For a large grouted wall, ask about bulk grout or ready-mix.

A standard normal-weight 8 x 8 x 16 block weighs about 37 lb; that is one block maker's listing, and others run a few pounds either way. Lightweight block is made with lighter aggregate: ASTM classes blocks by the concrete's density, with normal weight at 125 lb per cubic foot and up and lightweight under 105. Thinner blocks weigh less and 10 and 12 inch blocks more. The weight is usually on the tag or the supplier's spec sheet, and the calculator lets you enter it.

A pallet of 75 standard blocks is about 2,775 lb of block alone. Add 80 lb for each bag of mortar or grout.

Block is the heaviest thing most people try to fit in a pickup. A half-ton with a 1,150 lb payload carries about 31 standard blocks, and that is with nobody in the passenger seat. A full pallet (2,775 lb) is more than any half-ton payload (1,150 to 2,400 lb). The Haul Check above counts the trips; past two or three, delivery with a forklift or boom truck is usually worth it.

A block wall sits on a poured concrete footing, set below the frost line in cold climates. Work out its concrete with the footing option in the concrete calculator, and check local code for footing size, rebar, and when a wall needs a permit or an engineer. Tall and retaining walls almost always do.

• Plan the wall in 8 inch courses and 16 inch block lengths. Matching the layout to the block saves cutting. (Ernest Maier (block producer))
• An 80 lb bag of mason mix lays about 13 standard blocks. Mix only what you can lay before it stiffens. (QUIKRETE)
• Filling cores takes far more material than the mortar: one 80 lb bag of core-fill grout fills about 3 blocks. (QUIKRETE)
• A pallet of standard block can weigh well over a ton, so most block orders are a delivery.

• Laying out the wall on odd lengths. Plan in 16 inch steps and you avoid cutting a block in every course.
• Forgetting the core fill. It is heavier and more bags than the mortar.
• Not checking where the courses land. Courses come in 8 inch steps, so a wall planned at 3 ft is built at 3 ft 4 in or 2 ft 8 in.
• Loading a pallet of block into a half-ton pickup.
• Skipping the footing, or setting it above the frost line.