Cinder Block Calculator
Count before you haul. Enter the wall's length and height and this cinder block calculator returns the block count, the mortar bags to buy, and what the materials should cost.
Blocks needed
180
160 ft² wall
Mortar (80-lb bags)
6
≈ 35 blocks per bag
Est. materials cost
$384
blocks + mortar, no sand or tools
Add 5–10% extra blocks for breakage and cut courses — 193 blocks if you order 7% over.
Formula
Counts come from the nominal block face (8 × 16 in.):
blocks = wall length (ft) × height (ft) × 1.125 mortar bags = blocks ÷ 35 (80-lb bags, rounded up)
The 1.125 factor is exact geometry — one block per 0.889 ft² of wall. The 35-blocks-per-bag figure is a working rule of thumb; deep or raked joints use more.
Example
- A 20 ft × 8 ft wall is 160 ft².
- Blocks: 160 × 1.125 = 180 → 180 blocks (about 193 with a 7% cushion).
- Mortar: 180 ÷ 35 = 5.1 → 6 × 80-lb bags.
- At $1.60 per block and $16 per bag: 180 × 1.60 + 6 × 16 ≈ $384 in materials.
Frequently Asked Questions
How many cinder blocks do I need per square foot?
About 1.125. A standard 8×8×16 in. block covers a nominal 8 × 16 in. face — 0.89 ft² — so one square foot of wall takes 1.125 blocks, or 9 blocks per 8 ft². Suppliers count nominal sizes, mold dimensions are slightly smaller to leave mortar joints.
How many blocks does a bag of mortar lay?
An 80-lb bag of mortar mix lays roughly 35 standard blocks, which is the figure this calculator uses. Windy, dry conditions and deep joints use more — keep a spare bag on hand.
How much extra should I order?
Add 5–10% for breakage on site and the cut blocks at corners and openings. The calculator's order line already shows a 7% cushion; round up to the supplier's bundle size.
Does this include the concrete fill for block cores?
No — this estimates the blocks, mortar and their cost. Filling cores with concrete or grout (for retaining or structural walls) is priced separately: it depends on the block pattern and how many cores your engineer wants filled.