How to calculate concrete blocks
Standard block face = 8 × 16 in (nominal) = 0.889 sq ft → 1.125 blocks per sq ft
Example: a wall 20 ft long and 6 ft high is 120 sq ft. That's 135 blocks, plus 5% ≈ 142 blocks.
Nominal vs. actual size
A standard "8×8×16" block actually measures 7⅝ × 7⅝ × 15⅝ in. The missing ⅜ in is the mortar joint, so the nominal size is what you use to count blocks. The block's width (4, 6, 8, 10 or 12 in) doesn't change how many you need — only the face size matters.
How much mortar?
As a rough rule, one 80 lb bag of mortar mix lays around 13–14 standard blocks — about 7–8 bags per 100 blocks. Actual use depends on joint thickness and waste, so check the coverage printed on the bag and keep a spare.
Filling cores
If your design calls for grouted or rebar-filled cores, use our concrete calculator or ask your supplier for core-fill volume per block — it depends on the block width.
Frequently asked questions
How many concrete blocks per square foot?
1.125 standard 8 × 16 in blocks per square foot of wall (about 9 blocks per 8 sq ft).
How many blocks for a 10 ft by 8 ft wall?
80 sq ft × 1.125 = 90 blocks, plus 5–10% extra.
How much mortar for 100 blocks?
Roughly 7–8 bags of 80 lb mortar mix, depending on joints and waste.
Are cinder blocks and concrete blocks the same?
In everyday use, yes — most blocks sold today are concrete masonry units (CMU). True cinder blocks made with coal ash are rare now.
Related calculators
These figures are estimates for planning only. Material weights and coverage vary by supplier, moisture and compaction. Always confirm quantities and prices with your supplier before ordering. See our terms & disclaimer.