Concrete & Masonry
Concrete Block Calculator
Work out how many concrete blocks you need for a wall. Enter each wall’s length and height, subtract doors and windows, and this concrete block calculator counts the blocks (CMU or cinder blocks), pallets and bags of mortar, with an optional cost.
Result
Enter your measurements and press Calculate. What to buy, the working and the cost will appear here.
How to use the concrete block calculator
- Enter each wall: its length and height. Use How many for identical walls.
- Subtract openings by entering the total area of doors and windows.
- Choose the block size. 8 × 8 × 16 in is the standard CMU; pick Custom size for anything else.
- Check the joint and allowance, add blocks per pallet if you know it, and prices if you want a cost.
- Press Calculate for blocks, pallets and mortar.
How many concrete blocks do I need?
A standard block is 15 5/8 × 7 5/8 in; with a 3/8 in joint each one fills a 16 × 8 in space on the wall, which is 0.889 ft². So:
blocks = wall area (ft²) × 1.125
A 40 ft wall 4 ft high is 160 ft², so 160 × 1.125 = 180 blocks, plus 5% for cuts and breakage: 189 blocks.
Worked example: a garden wall with returns
A 4 ft high garden wall runs 40 ft along a boundary with two 12 ft returns. It is built from 8 × 8 × 16 in blocks at $2.10 each, with mortar at $9.50 a bag and blocks delivered 90 to a pallet:
- Wall 1: 40 ft × 4 ft = 160 ft²
- Wall 2: 12 ft × 4 ft × 2 = 96 ft²
- Blocks per ft²: 1 ft² ÷ (16 in × 8 in) = 1.125
- Blocks: 256 ft² × 1.125 = 288 × 1.05 = 302.4 → 303
- Mortar: 288 × 22.1 in³ × 1.25 = 4.61 ft³ ÷ 0.67 ft³ per bag → 7 bags
Blocks to buy: 303; Mortar: 7 bags of 80 lb mortar mix; Pallets: 4 pallets; Estimated cost: $702.80. Open this example in the calculator.
Blocks per square foot
| Block | Blocks per ft² | Blocks per 100 ft² |
|---|---|---|
| 8 × 8 × 16 in block | 1.13 | 113 |
| 6 × 8 × 16 in block | 1.13 | 113 |
| 12 × 8 × 16 in block | 1.13 | 113 |
| 4 × 8 × 16 in solid block | 1.13 | 113 |
All 16 in long blocks give the same count per square foot; the thickness (6, 8 or 12 in) changes the weight, strength and mortar, not the number.
How much mortar for concrete block?
Hollow blocks are usually laid on their face shells only, so they take much less mortar per block than bricks: roughly 2–3 bags of 80 lb mortar mix per 100 blocks, including waste. The calculator works it out from the joint size; the mortar calculator handles other units and bag sizes.
Buying and laying block
- Order corner, half and bond-beam blocks for corners, ends and the top course; ask your supplier, since the calculator counts standard blocks.
- Plan wall lengths in 8 in steps (half a block) to reduce cutting.
- Footings first. A block wall needs a solid concrete footing; estimate it with the footing calculator.
- Pallets of 8 in blocks commonly hold around 90 blocks and weigh well over a ton; confirm with your supplier and plan delivery access.
Assumptions and limitations
- Walls are rectangles; gables and stepped walls can be entered as several walls.
- Grout or concrete to fill cores, and rebar, are not included. Retaining walls and load-bearing walls need a design.
- Mortar assumes face-shell bedding for hollow blocks and full bedding for solid blocks.
Concrete block questions
How many blocks are in a square foot?
1.125 standard 8 × 16 in blocks (16 in × 8 in including the joint is 0.889 ft²). That is 112.5 blocks per 100 ft².
How many cinder blocks do I need for a 10 × 10 wall?
A 10 ft × 10 ft wall is 100 ft², so about 113 blocks, or 119 with 5% extra.
How many bags of mortar per 100 blocks?
Usually 2–3 bags of 80 lb mortar mix per 100 standard hollow blocks, depending on the joint, the bag yield and how much mortar is dropped.
Is a cinder block the same as a concrete block?
In everyday use, yes. True cinder blocks used coal cinders as aggregate; most blocks sold today are concrete masonry units (CMU), but the names are used interchangeably.
Formulas, unit conversions and default values are explained on our methodology page. Results are estimates; check manufacturer data and local codes before you buy or build.