Concrete block calculator
Blocks = wall area ÷ the face of one block with its mortar joint (16 × 8 in), plus extra: a wall 20 ft long and 4 ft high is 80 sq ft, or 90 blocks, 99 with 10% extra.
Example: replace these measurements
Your material list
99 concrete blocks+ 1 more item on the list
99 concrete blocks
80 sq ft measured
Your shopping list
- 99 concrete blocks
- 7 mortar bags
At posted store prices
- $395.01 99 × $3.99 a block, Standard concrete block, 8 × 8 × 16 in at Whiz-Q Stone in Fort Worth, TX on
- $83.93 7 × $11.99 a bag, QUIKRETE Mortar Mix 1102, 80 lb at Little Hardware in Charlotte, NC on
$478.94 for these 2 items, before tax and delivery.
Each price is one store’s posted price on the day shown, for the product named. Prices vary between stores: check yours. Your own price goes under Details.
Laid, this wall weighs about 2,000 to 3,100 lb, blocks and mortar together: NCMA’s table puts a hollow 8 in block wall at 25 lb a square foot in lightweight block and 39 lb in normal-weight block. That is roughly what the supplier will load into your truck, so before you haul it yourself, check the payload on the sticker in your truck’s door frame, or ask what delivery costs.
Quantities and package details
- Wall area after openings
- 80 sq ft
- Block positions before extra
- 90
- Mortar bags
- 7
- Core fill (from your design)
- Enter the blocks to fill
The calculation
- 80 ÷ ((15.63 + 0.38) × (7.63 + 0.38) ÷ 144) = 90 block positions
- 90 × (1 + 10/100), rounded up = 99 blocks
Common questions
How many concrete blocks per square foot?
About 1.125 for standard blocks. A block of 15 5/8 by 7 5/8 inches with a 3/8-inch mortar joint takes up 16 by 8 inches, which is 128 square inches, and a square foot is 144 square inches.
How much mortar do I need?
About one 80 lb bag for every 13 standard 8 × 8 × 16 in blocks: QUIKRETE says a bag of its Mortar Mix lays up to 13. A wall of 90 blocks takes 7 bags at that rate; buy one more for thicker joints and cut blocks.
Do I subtract doors and windows?
Yes, as square feet. Corners, ends and openings often need special blocks, which are ordered separately from ordinary blocks.
How many bags of grout fill concrete block cores?
QUIKRETE Core-Fill Grout fills the cores of about 3 standard 8 × 8 × 16 inch blocks an 80 lb bag, so 20 blocks take 7 bags. Which cores to fill, and the steel in them, come from your plan or engineer.
Source: QUIKRETE Core-Fill Grout – Coarse No. 1585-07 data sheet. Listed on the Sources page.
How to plan the quantity
Use actual face dimensions plus one mortar joint to get the repeating block position. The calculation divides net wall area by that position area, then adds your chosen allowance.
Corners, ends, bond beams and openings may need special units. Separate those from ordinary stretchers on the supplier order.
Mortar is counted from the blocks a bag lays: QUIKRETE gives up to 13 standard blocks for an 80 lb bag of its Mortar Mix or Mason Mix. Thick joints, cut blocks and a slow pace use more, so a spare bag is cheap insurance.
Before you order
- Area rounding does not produce a running-bond cut schedule or a structural design.
- Footings, reinforcement, grout-filled cores, lintels and wall stability need a design; they are not mortar-bag allowances.
Before ordering, read the guide: How much concrete do I need? Yards, bags and when to order a truck. Or choose another calculator.