Concrete Block Calculator

1.125 blocks per square foot, or 113 blocks per 100 square feet of wall. A standard block occupies a 16 × 8 in face once the ⅜ in mortar joint is included, which is 0.889 sq ft. This holds for 4, 6, 8, 10 and 12 inch block alike, because they all share the same face and differ only in thickness. Half-height 8 × 4 × 16 units double the figure to 2.25 per square foot. To turn that rate into a quantity, multiply it by the net wall area — length × height, less any openings — which is exactly what the calculator above does.

It depends which product you buy. Around three bags of masonry cement per 100 blocks if you are mixing with your own sand — plus roughly one cubic yard of sand per seven bags. Around nine 80 lb bags of pre-mixed mortar per 100 blocks if you are buying it ready-blended, which works out near 12 blocks a bag. The two figures look contradictory but describe different materials; check which one is sitting on your supplier's shelf before you order. Both rules assume a ⅜ in joint laid by someone who is not wasting it — a thicker joint, or a first wall, will use noticeably more cement and sand than the rule predicts.

Nominal size is the space the block occupies in the finished wall, joint included — 8 × 8 × 16 in. Actual size is the unit itself, 7⅝ × 7⅝ × 15⅝ in, exactly ⅜ in smaller in each direction so that one mortar joint brings it back to the module. Estimate with nominal dimensions and the arithmetic stays clean; estimate with actual dimensions and you will over-order by roughly 5%. Nominal sizing is also what makes masonry modular: every course adds 8 in of height and every unit 16 in of length, so a wall whose dimensions land on those increments needs almost no cutting.

Only where the design says so. A low garden wall usually stays hollow. A retaining wall, a tall freestanding wall or anything carrying load will have vertical rebar in specified cells, and those cells must be grouted solid to bond the steel into the wall. Common schedules are every fourth cell at 32 in centres, every other cell, or fully grouted for the heaviest cases. Grouting every cell "to be safe" is expensive and adds enormous weight to the footing — follow the engineer's drawing rather than guessing upward. Grout also adds weight the foundation has to carry — a fully grouted wall weighs close to double a hollow one — so changing the grout schedule after the footing is designed means the footing needs revisiting too.

Yes — masonry cannot be laid on soil. A block wall sits on a poured concrete foundation, typically twice the wall thickness in width and deep enough to reach below the local frost line, with dowels left standing wherever vertical reinforcement will run. The footing is a separate pour, a separate cost and often a separate trade, which is why no block quantity or material estimate on this page includes it. Two things are worth settling before that concrete goes off: the dowels have to line up with block cells, and the top of the footing should sit at a height that lets the wall rise in whole courses.

Roughly $15 to $30 per square foot installed in the United States in 2026 — materials $5–$13 and labor $10–$17. A 25 ft × 6 ft wall therefore runs about $2,250 to $4,500. Block is unusual in that labor outweighs material roughly two to one, so the biggest lever on cost is wall complexity — corners, openings, curves and cuts — rather than the price of the blocks themselves. Masonry construction is normally quoted by wall area rather than block quantity, so compare bids per square foot and check the material line against your own estimate. None of these figures include the concrete footing the wall has to sit on.

In everyday use, yes — and this calculator treats them identically. Historically a cinder block used coal cinders as the aggregate, making it lighter and considerably weaker; it has not been in general production for decades, and modern construction standards assume a concrete masonry unit throughout. What your supplier delivers today is made with sand and gravel aggregate, whichever of the two names appears on the invoice. The distinction only matters when you are matching or repairing genuinely old work, where the existing units really may be the weaker, lighter material.

Yes, deduct the full opening — that is standard estimating practice, and it is what this calculator does. Bear in mind that openings generate cutting waste along both jambs and often need special units such as bond beam or lintel block above them, so a wall with several openings deserves a higher waste allowance than a blank one. In practice: take each opening's area off the gross wall area, then let the waste percentage absorb the cutting it creates. On a wall that is mostly openings, price the lintels separately rather than trusting an area-based quantity at all.

An experienced mason with a labourer keeping them supplied will lay somewhere around 150 to 250 standard blocks in a day on a straightforward wall; a competent DIYer should plan on a third of that, and less on the first day. Corners, openings and grouting all slow it down sharply. Divide the block quantity from this calculator by a realistic daily rate to sanity-check how long a quote says the job will take. Masons often plan the day in courses rather than blocks, since finishing a full course around the wall is a natural stopping point and keeps the whole length rising evenly.