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Concrete Block Calculator
How many concrete blocks (cinder blocks, CMUs) do you need for a wall, garden bed or foundation? Enter the size to get the block count, mortar and cost.
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Estimate only. Bag yields, material density and waste vary by product and supplier. Confirm quantities with your supplier and check local building codes before you buy or build.
How many blocks per square foot?
A standard 8 × 8 × 16 inch concrete block, also called a CMU, covers 128 square inches of wall including the mortar joint. That is 1.125 blocks per square foot, or about 112.5 blocks per 100 square feet.
How to calculate blocks for a wall
Multiply wall length by height for the area, subtract doors and windows, then multiply by 1.125. A 20 × 4 ft wall is 80 square feet, or 90 blocks. Add 5 to 10% for breakage and cuts, which makes 99.
How much mortar do I need?
Plan on roughly 3 bags of 80 lb mortar mix per 100 blocks for standard 3/8 inch joints. Mortar use varies with joint thickness and mason, so treat it as an estimate and buy a bag or two extra.
Frequently asked questions
How many concrete blocks do I need for a 20 ft wall?
At 4 feet high a 20 ft wall takes 90 standard blocks, 99 with 10% extra. At 8 feet high it takes 180, or 198 with extra.
Is a cinder block calculator the same as a concrete block calculator?
Yes. Cinder block is the everyday name for a concrete masonry unit (CMU). Modern blocks are concrete, not cinders, but the sizes are the same: an 8 × 8 × 16 block covers 1.125 per square foot of wall.
How many cinder blocks are in a pallet?
A pallet of standard 8 × 8 × 16 blocks often holds 75 to 90, depending on the supplier. Ask for the exact count when ordering.
Do the block dimensions include the mortar joint?
The nominal size of 8 × 8 × 16 includes a 3/8 inch joint. The actual block is about 7 5/8 × 7 5/8 × 15 5/8 inches. The calculator uses the nominal face, which is what a laid wall occupies.
Does this include filling the cores or rebar?
No. This estimates blocks and mortar only. Grout, rebar and core fill depend on your wall design and local code.
How accurate is this estimate?
It is a planning estimate, not an order. Bag yields, material density and waste vary by product, supplier and job, so confirm quantities with your supplier and check local building codes before you buy or pour.
Are my measurements saved?
No. Everything is calculated in your browser. Nothing is uploaded or stored.
