How Many Cinder Blocks Do I Need? (2026)

To find how many cinder blocks you need, multiply your wall area in square feet by 1.125 for standard 8x8x16 inch blocks, then add about 10% for waste. That works because one block plus its mortar joint covers 0.89 square feet of wall face. Here is the formula, worked examples, mortar amounts, and a calculator that does the counting for you.

The formula: blocks per square foot

Cinder block walls are counted by area, not volume. A standard block is sized 8 by 8 by 16 inches nominal, which already includes the mortar joint, so its face plus mortar covers a tidy 8 by 16 inch rectangle. That works out to 0.89 square feet, and dividing 1 by 0.89 gives 1.125 blocks per square foot of wall.

Blocks = Wall length(ft) × Wall height(ft) × 1.125

So a wall 50 feet long and 8 feet high is 400 square feet, which is about 450 blocks. Add a 5 to 10% waste allowance for cuts and breakage and you order around 495. To skip the arithmetic, the cinder block calculator turns your wall size straight into a block count.

Nominal vs actual block size

Always plan with the nominal size, not the physical one. A block marked 8 by 8 by 16 inches actually measures 7 5/8 by 7 5/8 by 15 5/8 inches, which is 3/8 inch smaller in each direction. That missing 3/8 inch is exactly the mortar joint, so one block plus one joint returns to the full nominal 8 by 16 inch module.

These sizes are set by ASTM C90, the standard for load-bearing concrete masonry units, which allows a tolerance of about 1/8 inch. The width is the part that names the block: a 6 inch block is 6 inches wide, a 12 inch block is 12 inches wide, and both still measure 8 inches high and 16 inches long.

How many blocks for a wall, by size

The table below uses the 1.125 multiplier with a 10% waste allowance already added, so the counts are what you would actually order. Subtract any door or window openings from your area first, then apply the multiplier to the net figure.

Wall (length x height)	Area (sq ft)	Blocks (+10%)
10 x 8 ft	80	99
20 x 8 ft	160	198
40 x 8 ft	320	396
50 x 8 ft	400	495
100 x 6 ft	600	743

Different block heights change the multiplier. A 4 inch high block needs 2.25 per square foot, double the standard count, because it covers half the face area of an 8 inch high block.

How much mortar you need

The masonry rule of thumb is about 3 bags of mortar per 100 blocks at a standard 3/8 inch joint. An 80 lb bag of pre-mixed Type N or Type S mortar lays roughly 12 to 13 standard blocks, and a 60 lb bag lays about 10. By volume that is close to 9.5 cubic feet of mortar for every 100 blocks.

Match the mortar to the job. Type N (about 750 psi) suits above-grade, non-load-bearing walls, while Type S (about 1,800 psi) is the choice below grade or for retaining walls, per ASTM C270. Using Type N below grade risks joint failure from freeze and thaw.

If you are buying dry ingredients, plan on about one cubic yard of sand for every 7 bags of mortar. The concrete calculator helps if you also need to pour a footing under the wall before the first course goes down.

A pallet of grey cinder blocks on a job site next to a partly built concrete block wall

What cinder blocks cost in 2026

Standard 8 by 8 by 16 inch hollow blocks run about 1.25 to 2.50 dollars each in 2026 at home centers. Solid or split-faced blocks cost more, roughly 2 to 5 dollars apiece, and the larger 12 inch blocks land around 2 to 4 dollars each.

Buying by the pallet is cheaper per block. A pallet holds 70 to 90 blocks and costs 115 to 225 dollars, weighing 2,500 to 3,250 pounds, so plan delivery rather than hauling it yourself. Each block weighs 28 to 36 pounds, which adds up fast on a big wall.

Tips so you do not run short

The most common mistake is forgetting waste. Cut blocks at corners, around openings and at wall ends, plus the odd cracked unit, mean you should always add 5 to 10% and round up to whole blocks. Coming up two blocks short on the last course means a second trip and a mismatched batch.

The second mistake is measuring the opening but not subtracting it. Work out the gross wall area, subtract the area of every door and window, then apply the 1.125 multiplier to what is left. For a wall that steps or turns corners, count each straight run separately and add them, then let the cinder block calculator tally the blocks, mortar and cost in one pass.

How we check this

Every formula is shown in full and verified with automated tests against manufacturer spec sheets and ASTM and ACI standards. We show our work so you can check it.

Cost estimate, not a quote. The prices here are ballpark figures for planning only. Real costs vary by region, supplier, season, site access and project size. Always get written quotes from local contractors before you set a budget.

Frequently asked questions

How many cinder blocks do I need per square foot?

You need 1.125 standard 8x8x16 inch cinder blocks per square foot of wall, because each block plus its 3/8 inch mortar joint covers 0.89 square feet. Multiply your wall area by 1.125 and add 5 to 10% for waste.

How many cinder blocks are in a 10x10 wall?

A 10 by 10 foot wall is 100 square feet, so it needs about 113 standard blocks before waste, or roughly 124 with a 10% allowance. Subtract any openings from the area first.

How many bags of mortar do I need per 100 blocks?

Plan on about 3 bags of mortar per 100 standard 8x8x16 blocks at a 3/8 inch joint. An 80 lb bag lays roughly 12 to 13 blocks and a 60 lb bag about 10.

How much do cinder blocks cost in 2026?

Standard 8 inch hollow cinder blocks cost about 1.25 to 2.50 dollars each in 2026, while a full pallet of 70 to 90 blocks runs 115 to 225 dollars. Solid and split-faced blocks cost more.

What is the difference between nominal and actual block size?

Nominal size includes the mortar joint and actual size is the physical block. An 8x8x16 nominal block actually measures 7 5/8 by 7 5/8 by 15 5/8 inches. Always plan with the nominal size.

How Many Cinder Blocks Do I Need?

Key takeaways