How to Calculate How Many Cinder Blocks You Need

May 31, 2026

What You Need Before You Start

Wall length and height in feet (or total square footage)
Number and dimensions of any door or window openings
Block size — 8×8×16 for most structural walls
Whether you want a material cost estimate

Step 1 — Measure Your Wall Area

Measure the length and height of your wall in feet. Multiply to get gross wall area.

Wall area = Length (ft) × Height (ft)

Example: 24 ft long × 8 ft high = 192 sq ft

For multiple walls (such as a rectangle or U-shape), measure each wall separately and add the lengths together before multiplying by height — as long as all walls are the same height.

Step 2 — Subtract Door and Window Openings

For each opening, multiply its width × height in feet and subtract from the gross wall area.

Example:

1 door: 3 ft × 7 ft = 21 sq ft
1 window: 3 ft × 4 ft = 12 sq ft
Total openings: 33 sq ft

Net wall area = 192 − 33 = 159 sq ft

If your wall has no openings, skip this step.

Step 3 — Calculate Raw Block Count

For standard 8×8×16 cinder blocks with a 3/8-inch mortar joint, you need 1.125 blocks per square foot.

Raw block count = Net wall area × 1.125

Example: 159 × 1.125 = 178.9 → 179 blocks

Always round up — you cannot order a fraction of a block.

Step 4 — Add Waste

Waste accounts for blocks cut to fit corners, edges, and openings, plus any breakage during handling.

Project type	Waste factor
Simple straight wall, no cuts	5%
Standard wall with some cuts	10% (recommended)
Complex wall, many corners/openings	15%

Example (10% waste): 179 × 1.10 = 196.9 → 197 blocks

Order to the next full pallet if possible. A standard pallet holds 90 blocks (8×8×16), so round up to the nearest 90. For 197 blocks: order 3 pallets (270 blocks) or buy 207 individual blocks.

Step 5 — Calculate Number of Courses

Courses are the horizontal rows of blocks stacked to reach your wall height. For 8×8×16 blocks with a 3/8-inch joint, each course is 8.375 inches tall.

Courses = Wall height (in) ÷ 8.375

Example: 8 ft = 96 in ÷ 8.375 = 11.46 → 12 courses

Always round up to the nearest whole course. 12 courses × 8.375 = 100.5 inches = 8.375 ft — your wall will be very slightly taller than your target. Plan your top bond beam accordingly.

Step 6 — Calculate Mortar

For standard 80 lb pre-mixed mortar bags, use 8.5 bags per 100 blocks as your rule of thumb.

Mortar bags = (Total blocks ÷ 100) × 8.5

Example: (197 ÷ 100) × 8.5 = 16.7 → order 17 bags

Step 7 — Estimate Cost

Use local prices — cinder block prices vary significantly by region and supplier.

Material	Quantity	Typical unit price	Estimated cost
Cinder blocks	197	$2.00–$3.50 each	$394–$690
Mortar (80 lb bags)	17	$6–$9 per bag	$102–$153
Materials total			$496–$843

Add 20–30% for sand fill, rebar, block caps, concrete footings, and miscellaneous hardware. Labor (if hiring) typically runs $8–15 per block installed.

Quick Reference

For an 8 ft tall wall (most common):

Wall length	Blocks (with 10% waste)	Mortar bags	Courses
10 ft	101	9	12
20 ft	202	17	12
30 ft	303	26	12
40 ft	405	34	12
50 ft	506	43	12

Common Mistakes

Forgetting waste — Always add at least 10%. Buying extra is cheap. Running short mid-project means delays and potential mismatched block batches.

Using interior dimensions for hollow blocks — For hollow-core blocks, the mortar goes on the face shells only, not the full block width. Pre-mixed mortar quantities already account for this.

Ignoring actual vs nominal height — 12 courses of 8×8×16 = 100.5 inches, not 96 inches. If your wall has a specific height requirement, work backwards from the course height to hit it exactly.

Ordering too many pallets without checking delivery access — A full pallet of 90 blocks weighs roughly 1.5 tons. Confirm your delivery vehicle can access your site before ordering large quantities.