How to Use the Concrete Block Calculator
This concrete block calculator helps you estimate how many concrete blocks (CMU — concrete masonry units) you need for any wall project. Follow the steps below:
- Choose a unit system — Imperial (feet/inches) or Metric (meters/mm).
- Enter wall dimensions — input the wall width and wall height.
- Select block size — pick one of the six common CMU presets or enter a custom block size.
- Adjust mortar joint — the default is ⅜ inch (9.5 mm). Change it if your project uses a different joint thickness.
- Optional: enter the price per block and choose your currency to get a total material cost estimate.
- Click Calculate to see the results instantly.
How Many Concrete Blocks Do I Need?
The calculation is straightforward:
- Wall area = wall width × wall height
- Block face area = (block height + mortar joint) × (block width + mortar joint)
- Number of blocks = wall area ÷ block face area (rounded up)
- Mortar bags estimate = number of blocks ÷ 33.3 (rounded up)
Rule of thumb: 3 standard mortar bags per 100 blocks.
Calculating Concrete Blocks — Example
Suppose you are building a wall 20 ft wide and 8 ft tall using the standard 8"×16" CMU block with a ⅜" mortar joint:
- Wall area = 20 × 8 = 160 ft²
- Unified wall area = 160 × 144 = 23,040 in²
- Block face area = (7.625 + 0.375) × (15.625 + 0.375) = 8 × 16 = 128 in²
- Blocks needed = 23,040 ÷ 128 = 180 blocks
- Mortar bags = ⌈180 ÷ 33.3⌉ = 6 bags
The Six Standard CMU Block Sizes (U.S.A.)
| Preset | Nominal (H × L) | Actual (H × L) |
|---|---|---|
| Standard | 8" × 16" | 7⅝" × 15⅝" |
| Half block | 8" × 8" | 7⅝" × 7⅝" |
| Small 4×8 | 4" × 8" | 3⅝" × 7⅝" |
| Thin 4×16 | 4" × 16" | 3⅝" × 15⅝" |
| Large 12×16 | 12" × 16" | 11⅝" × 15⅝" |
| Jumbo 8×12 | 8" × 12" | 7⅝" × 11⅝" |
A Note on Using the Concrete Block Calculator
Keep in mind that this calculator gives you a base estimate without wastage. In practice, always add 5–10% extra blocks to account for cuts and breakages. The mortar bags estimate (3 bags per 100 blocks) is also an approximation — actual mortar usage depends on joint thickness and application method.
For hollow core blocks (CHBs), you may also need to fill the voids with mortar or grout. Use a separate concrete fill calculator for that purpose.
FAQs
- What is the most common concrete block size?
- In the USA, the standard CMU is 8" × 8" × 16" nominal (7⅝" × 7⅝" × 15⅝" actual). It is the go-to block for load-bearing and non-load-bearing walls.
- How many standard concrete blocks are in a square foot?
- One standard 8"×16" block (with ⅜" mortar joint) covers exactly 1.125 ft² (128 in²). That means approximately 1.13 blocks per square foot, or about 113 blocks per 100 ft².
- Can I use this for cinder blocks?
- Yes. Cinder blocks share the same nominal dimensions as concrete blocks. The calculator works equally well for both.
- What currencies does the cost estimate support?
- The calculator supports 20 major world currencies: USD, EUR, GBP, CAD, AUD, CHF, JPY, CNY, INR, RUB, BRL, MXN, KRW, SGD, HKD, TRY, SEK, NOK, PLN, and ZAR.