How many blocks are in a square foot of wall?

About 1.125 standard 8-by-16-inch blocks per square foot, once the mortar joint is counted. So a 100-square-foot wall needs roughly 113 blocks before adding waste.

How much mortar do I need per 100 blocks?

Plan on roughly three 80-lb bags of masonry mortar per 100 standard blocks. Thick joints or deep hollow units can push it toward four.

How much waste should I add?

Around 5% for a plain straight wall. Add closer to 10% if the wall has many corners, curves or lots of small openings that force extra cuts.

Do I subtract windows and doors from the count?

Yes. Subtract each opening's area from the gross wall area first, then calculate blocks from the net figure — otherwise you will badly over-order.

How Many Concrete Blocks Do I Need? Blocks, Mortar and Waste

Published 2/11/2026 · 3 min read · Real-estate calculators

Marco Bianchi — Home, DIY & motoring writer at Allin

Renovation · Materials

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In short

Divide the wall area by the face area of one block to get the raw count. A standard 8-by-16-inch block covers about 0.89 sq ft with its mortar joint, so it takes roughly 1.125 blocks per square foot of wall. Add about 5% for cuts and breakage, and budget roughly three 80-lb bags of mortar per 100 blocks.

Concrete blocks laid out in regular rows, seen close up. — Jan van der Wolf · Pexels · Pexels

Work out how many concrete blocks a wall needs from its area, add mortar and a waste allowance, and avoid a second trip to the yard.

Start from wall area, not block count

The reliable way to size a block order is by area. Measure the wall's length and height, multiply for the gross area, then subtract every door and window opening. What remains is the net area you actually have to fill with masonry.

A standard concrete block measures 8 by 16 inches on its face, and with a 3/8-inch mortar joint it effectively covers about 0.89 sq ft. That works out to roughly 1.125 blocks per square foot, so a 100-square-foot wall needs about 113 blocks before waste.

Add mortar and a waste margin

No wall uses only whole blocks. Corners, openings and the top course all need cut pieces, and a few blocks always crack in handling. A 5% allowance is a sensible default for a straightforward wall; add closer to 10% for lots of corners or curved layouts.

For mortar, a common working figure is about three 80-lb bags of masonry mortar per 100 standard blocks. Thick joints, deep hollow units or rough weather that dries the mix quickly all push that number up, so round bags up rather than down.

Sanity-check before you order

Blocks are cheap individually but heavy and awkward to fetch a second time, so it pays to order slightly long rather than short. Leftover whole blocks are easy to return or reuse, whereas running out mid-course stalls the whole job.

Also confirm the exact block your supplier stocks: nominal sizes vary, and a half-height or a thinner partition unit changes the count per square foot. The calculator lets you set the block face so the estimate matches what you will actually buy.

Worked with our own calculator

Concrete blocks calculator

Given

Wall area (m²): 22
Block length (cm): 44
Block height (cm): 22
Waste (%): 10

Result

Blocks needed: 251

These figures are produced by the calculator below, not typed in by hand — they are recomputed whenever the tool changes.

Run it on your own figures →

Frequently asked questions

How many blocks are in a square foot of wall?: About 1.125 standard 8-by-16-inch blocks per square foot, once the mortar joint is counted. So a 100-square-foot wall needs roughly 113 blocks before adding waste.
How much mortar do I need per 100 blocks?: Plan on roughly three 80-lb bags of masonry mortar per 100 standard blocks. Thick joints or deep hollow units can push it toward four.
How much waste should I add?: Around 5% for a plain straight wall. Add closer to 10% if the wall has many corners, curves or lots of small openings that force extra cuts.
Do I subtract windows and doors from the count?: Yes. Subtract each opening's area from the gross wall area first, then calculate blocks from the net figure — otherwise you will badly over-order.

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