Concrete Block Calculator
This concrete block calculator tells you how many blocks a wall needs. Enter the length and height, set the block face size, note any openings and a waste margin, and you'll get the blocks, mortar bags, and cost. Everything updates as you type, so it's easy to plan a garden wall, foundation, or block shed. It's free and runs in your browser, so pricing a block job takes seconds.
- Blocks for a wall
- Mortar bags
- Wall area
- Subtracts openings
- Cost estimate
Last updated June 17, 2026 Feet, by wall area Reviewed by the Calcowa team
Enter a wall size and block size above zero.
A standard block has a 16 by 8 inch face, about 0.89 sq ft, so roughly 1.13 blocks cover a square foot. Mortar runs about 3 bags per 100 blocks. Leave the price blank to skip the cost line.
How do you calculate how many concrete blocks you need?
Block walls go up one course at a time, so the job is to turn a wall into blocks, and it's not as fiddly as it sounds. First you find the wall area: the length times the height in feet. Take off any door and window openings, since you won't lay block there, then add a small waste margin, often 5 to 10 percent, because blocks chip and crack when they're cut. Now divide that area by the face of one block. A standard 16 by 8 inch face covers about 0.89 square feet, so you get roughly 1.13 blocks per square foot, and you round up. This tool runs every step, so you'll get a block count, a mortar estimate, and a cost the moment you type the wall size, and you don't have to count courses by hand. If you're only building a short garden wall, that's fine too, since you can drop the height right down.
Estimating a wall, step by step
Here's the quick routine before you order, and it's just three steps:
- 1
Enter the wallType the length and height, and any openings.
- 2
Set block and wasteChoose the block face size and a waste margin.
- 3
Read the blocksSee the blocks, mortar bags, and cost you'll need.
Blocks by wall area
Here's a rough guide for standard 16 by 8 inch blocks and 5 percent waste. It's a starting point, so don't treat it as exact, since your block size and openings won't match every job. When you're ready, run your own numbers above.
| Wall | Wall sq ft | Blocks |
|---|---|---|
| 10 x 10 ft | 100 | 119 |
| 20 x 8 ft | 160 | 189 |
| 25 x 8 ft | 200 | 237 |
| 40 x 8 ft | 320 | 378 |
Frequently asked questions
You enter the wall size, the block face size, and a small waste margin, and it works out the blocks, mortar, and cost. It finds the wall area from the length and height, subtracts any door or window openings, adds the waste, then divides by the face area of one block. Everything runs in your browser, so you'll see the block count change as you adjust a number, and you can copy the result to take to the supplier.
Find the wall area in square feet, take off the openings, add about 5 to 10 percent for waste, then divide by the face of one block. A standard 8 by 8 by 16 inch block covers roughly 0.89 square feet of wall, which works out to about 1.13 blocks per square foot. A 20 by 8 foot wall needs around 189 blocks once you allow for waste, and the calculator does that math the moment you type the wall size.
For the common 8 by 16 inch block face, it's about 1.13 blocks per square foot, since one block covers roughly 0.89 square feet including the mortar joints. A taller or shorter block changes that, which is why this tool lets you set the face size yourself. Half-height or jumbo blocks cover a different area, so the per-square-foot figure shifts, and the block count follows along automatically as you type.
A rough rule is about 3 bags of mortar per 100 blocks, so a 200 block wall takes around 6 bags. That covers standard joints with a premixed mortar, though tall walls, wide joints, and cold weather all change it. The calculator gives you a mortar estimate from the block count, but treat it as a starting point and pick up an extra bag or two, since running short mid-course is a real headache.
Yes, a small surplus is smart, because blocks chip on delivery, crack when cut, and a few always come damaged. The waste margin here defaults to 5 percent, but bump it toward 10 percent for a wall with lots of corners, ends, or cuts around openings. Blocks from a later batch can differ slightly in color and texture, so it's better to have a couple spare than to make a second trip for the same lot.
Yes, it's completely free, with no sign-up, and it runs right in your browser, so nothing you enter leaves your device. Type the wall size, set the block and waste, and read the blocks in a tap. Bookmark it for a garden wall, a foundation, or a block shed, and you'll have a solid block estimate whenever you plan a concrete block project.
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