Construction tool

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 loads instantly in the page, so pricing a block job takes seconds.

Blocks for a wall
Mortar bags
Wall area
Subtracts openings
Cost estimate

Last updated July 31, 2026 Feet, by wall area Reviewed by the Calcowa team

Blocks needed

189 blocks

160

Wall sq ft

1.13

Blocks/sq ft

Mortar bags

–

Cost

Wall length (feet) Wall height (feet) Openings (sq ft)

Block size Waste (%) Price per block ($)

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.

The basics

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.

blocks = ceil(wall area × waste ÷ block face)

The names throw a few people, but a concrete block, a cinder block, a cement block, and a CMU all mean the same hollow masonry unit, so the count comes out the same whichever word your yard uses. Here's the default wall worked through: a 20 by 8 foot wall is 160 square feet. With no openings and a 5 percent waste margin, that's 168 square feet of block to buy. Divide by the 0.89 square foot face of a standard block and you get 189 blocks, plus about 6 bags of mortar at roughly 3 bags per 100 blocks. Knock out a 3 by 7 foot doorway and the wall drops to 139 square feet, so you'd need around 165 blocks instead. Not sure of the wall area yet? The square footage calculator sorts that first.

Step by step

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.

Quick reference

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

Coverage by block size

Switch the block size and the count moves, since a bigger face covers more wall per unit. Here's how many blocks each common size covers, in both square feet and square meters, so you can sanity-check the tool or work in metric.

Block size (in)	Face area	Blocks / sq ft	Blocks / m²
8 x 8 x 16 (standard)	0.89 sq ft	1.13	12.1
8 x 8 x 12	0.67 sq ft	1.50	16.1
8 x 4 x 16 (half-height)	0.44 sq ft	2.25	24.2
8 x 8 x 18 (jumbo)	1.00 sq ft	1.00	10.8

Figures use the nominal face (block plus a 3/8 inch mortar joint) and round for quick use. Filling the hollow cores with grout is a separate pour, not counted here.

FAQ

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 loads instantly in the page, 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.

For this calculator, yes. Cinder block, cement block, CMU, and concrete block all name the same hollow masonry unit, so the block count works the same whichever term your supplier uses. The math is wall area divided by the face of one block, so it holds in metric too: a standard 16 by 8 inch block covers about 0.083 square meters, which is roughly 12 blocks per square meter.

No, it counts the blocks, mortar, and cost, not the grout that fills the hollow cores. Core fill is a separate volume, since only some walls get filled, and how much you pour depends on how many cores you fill and whether there's rebar inside. Work out the block count here first, then size the fill with the concrete calculator, which handles cubic yards and bags for the pour.

Yes, it's completely free, with no sign-up, and it runs right in your browser, so none of your numbers are stored. 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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