Concrete Block Calculator
Estimate exactly how many concrete blocks (CMU) and bags of mortar your wall needs. Enter the wall dimensions, pick a block size, subtract any door or window openings, and get an instant block count, mortar estimate and optional cost breakdown — with a live wall drawing and a printable PDF report.
Material cost estimate (optional)
How to estimate concrete blocks for a wall
Three quick steps from wall dimensions to a block count and mortar order.
Enter the wall's length and height in feet, inches, yards or metres. If you're pricing several identical walls, set the number of walls so the total scales automatically.
Choose the block thickness (4″–12″), confirm the mortar joint (3/8″ is standard), and enter the combined area of any doors or windows to subtract from the wall.
See the total blocks to order, bags of mortar, the coursing layout (rows × blocks per row), and an optional cost breakdown — ready to export as a PDF.
Concrete Block Calculator — Free & Accurate
Our concrete block calculator helps masons, contractors and DIYers work out exactly how many CMU (concrete masonry unit) blocks a wall needs, along with the mortar to lay them. Enter the wall's length and height, pick a block size, subtract any doors or windows, and get an instant block count, mortar estimate and optional cost in seconds.
Block count comes straight from the wall's net area: a 20 ft long, 8 ft high wall has an area of 160 ft². Standard CMU has an actual face of 15⅝″ × 7⅝″, which becomes a nominal 16″ × 8″ once the standard 3/8″ mortar joint is added — that works out to 1.125 blocks per square foot, so the 160 ft² wall needs roughly 180 blocks before waste. This ratio holds for every standard block thickness (4″ through 12″), since only the block's depth changes, not its face — the thickness you pick affects the wall's structural width, not how many blocks cover it.
Mortar is estimated using the common trade rule of roughly 36 standard 8×8×16 blocks per 80 lb bag of pre-blended Type S mortar mix, scaled for your chosen face size and joint thickness. Results also show the coursing — how many rows high the wall is and how many blocks sit in each row — so you can sanity-check the layout before ordering. An optional cost section covers block, mortar and labor pricing in USD, GBP, EUR, AUD, CAD, INR, BDT or AED. Everything runs in your browser — no signup, no data sent anywhere.
Why use this calculator?
Built for the block wall — simple, fast, and accurate.
No spreadsheets, no coursing tables. Type your wall dimensions, hit calculate — block count, mortar bags and coursing on screen in an instant.
4″, 6″, 8″, 10″ and 12″ CMU presets, plus a custom face-size option for non-standard or half blocks.
Subtract the combined area of doors and windows so you don't over-order blocks for openings you're not filling.
Add block, mortar and labor prices for a project estimate in 8 currencies — per block, per 100, per bag, hourly or flat-fee.
Everything runs in your browser. Your dimensions, prices and cost data never leave your device.
Mix feet, inches, yards, metres and centimetres on the same job. Fully responsive — open it on your phone right on the job site, no app needed.
Related construction tools
The block calculator pairs naturally with these — from footing to finish.
Frequently asked questions
The short, practical answers to the questions masons and DIYers ask most.
Multiply the wall's length by its height to get the area, subtract any doors or windows, then multiply by 1.125 blocks per square foot — the standard coverage for an 8×16 in face block with a 3/8″ mortar joint. A 20 ft × 8 ft wall (160 ft²) needs roughly 180 blocks before waste. Add 5–15% wastage on top for cuts, breakage and corners, and always round up to the next full block.
A common trade rule is that one 80 lb bag of pre-blended Type S mortar mix lays about 36 standard 8×8×16 blocks. This calculator scales that figure to your chosen block face and mortar joint, then rounds up to the next full bag. Bag coverage varies by brand and by how thick a bed you lay, so confirm the exact yield printed on your mortar mix bag before ordering in bulk.
No. Standard CMU blocks share the same 16″ × 8″ nominal face regardless of thickness — only the block's depth (4″ through 12″) changes, which sets the wall's structural width, not how many blocks cover its surface. So a 4″ partition wall and a 12″ load-bearing wall of the same length and height need the same block count, just heavier, thicker blocks for the 12″ version.
Add up the width × height of every door and window opening in the wall and enter the total in the Openings field — the calculator subtracts it from the gross wall area before converting to blocks. This avoids ordering blocks for space you won't be filling. Note that openings still need a lintel or bond beam above them, which isn't covered by this tool.
5% is reasonable for a simple, straight wall with no corners; 10% is a safe default for most jobs with a corner or two; 15% suits complex layouts with many corners, half-blocks or cut blocks around openings. Concrete block is heavy and breakage happens on delivery and handling, so it's always cheaper to order a few extra than to pause a course waiting on a second delivery.