Concrete Block Calculator
Calculate how many standard 16x8 in CMU concrete blocks you need for a wall from its length and height, plus mortar estimates.
How this calculator works
A standard concrete block (CMU) measures 16 in x 8 in nominally, giving an exposed face of about 0.888 sq ft — close to the commonly cited “1.125 blocks per square foot” figure. This calculator divides your wall area by that face size to get the block count, rounding up since blocks are bought as whole units.
Formula: Blocks = Wall area (sq ft) ÷ 0.888 sq ft per block.
Worked example
A wall 20 ft long x 8 ft high (160 sq ft):
- Area: 20 x 8 = 160 sq ft
- Blocks: 160 ÷ 0.888 ≈ 180.1802 → rounds up to 181 blocks
- At $2.50/block, that’s $452.50 before waste.
- Mortar: at ~3 bags per 100 blocks, 181 blocks ≈ 5.4 bags.
Coverage reference
| Wall area | Blocks needed (~1.125/sq ft) |
|---|---|
| 80 sq ft | 91 blocks |
| 160 sq ft | 181 blocks |
| 300 sq ft | 338 blocks |
How to measure your wall
Measure the wall’s full length and height in feet — length goes in the Length field, height in the Width field. For walls with door or window openings, subtract the opening’s area from the total for a tighter count, though the waste allowance usually covers small openings without extra math.
Frequently asked questions
How many concrete blocks do I need for a wall?
A standard 16 in x 8 in CMU (concrete masonry unit) has an exposed face of about 0.888 sq ft, which works out to roughly 1.125 blocks per square foot. Enter your wall's length and height and this calculator gives you the block count directly, rounded up to a whole block.
Should I enter length and height, or length and width?
For a wall, put the wall's length in the Length field and its height in the Width field — the calculator just multiplies the two to get area, so it doesn't matter which physical dimension goes in which field as long as one is length and one is height.
How much mortar do I need for a block wall?
A common rule of thumb is about 3 bags of mortar mix per 100 blocks, for standard 3/8 in mortar joints. That scales linearly, so a 181-block wall (this calculator's default) needs roughly 5.4 bags — round up to whole bags and add a margin for a first-time pour.
How much waste should I add for concrete block?
5-10% is standard, covering broken blocks, cuts at corners, openings, and course-height adjustments. Walls with lots of window or door openings, or courses that don't divide evenly into your wall height, may need more.
Does this include rebar or grout fill for the block cores?
No — this calculator counts face-count blocks only. Reinforced or grout-filled block walls (common for load-bearing and retaining walls) need separate rebar and grout takeoffs based on your engineering spec, typically figured per vertical core spacing.
Is 0.888 sq ft the exposed face for every concrete block size?
No — 0.888 sq ft is specific to the standard 16 in x 8 in (nominal) CMU face, the most common size for residential and light commercial walls. Half-blocks, corner blocks, and other nominal sizes (like 12x8 or 16x4) have different face areas, so adjust your block count if you're using a non-standard size.
Estimates only. Verify quantities with your supplier before purchasing.