Concrete Block Calculator

Concrete Block Calculator

This concrete block calculator is a free material estimator for ordinary rectangular CMU, cinder, and hollow block walls.

No signup
Multiple walls
Opening deductions

Blocks to Buy

198

180 base + 18 waste

Unit:

Wall 1

Openings (0)
Openings (Doors & Windows)

Block, waste, and price settings

8×8×16 Standard · 0 openings · 10% waste

Nominal Block Size

Presets and custom values use nominal module dimensions. Do not add the mortar joint again.

Waste Allowance10%

10% is an editable planning allowance. Adjust it for your layout, cuts, and breakage.

Cost Estimation

Enable to enter local block and 60-lb premix bag prices and see estimated cost.

Does this concrete block calculator already subtract doors and add waste?

Blocks to buy already subtracts the openings you entered, then adds one waste allowance for the whole project. This concrete block wall calculator lists base blocks and waste separately so you can check both before you order.

A 24 x 8 ft wall is 216 blocks if you divide the full face by 0.89 sq ft per block. Subtract the 9 x 7 ft garage opening from the example below and the same wall is 146 base blocks, then 161 to buy at 10% waste. 216 still counts the door.

Calculate concrete blocks in four steps:

  1. Gross wall area = wall length × wall height.
  2. Net wall area = gross wall area − door, window, and custom opening areas.
  3. Base blocks for each wall = net wall area ÷ nominal face module area, rounded up to a whole block.
  4. Blocks to buy = the sum of base blocks for all walls × (1 + waste percentage), rounded up once for the project.

If you only multiply length by height, or divide that area by 0.89 sq ft, you still count the door.

Miss an opening and you pay for unused blocks. Skip waste and you can run short mid-job.

  • See gross area, openings, and net area before you round
  • Round whole base blocks per wall, then apply project waste once
  • Use the live schematic to see what drove the order total
This live schematic uses the current calculator facts. It supports a material estimate and does not provide a bond layout, cut list, reinforcement, or structural advice.

The default 10% is an editable planning allowance for cuts and breakage, not a universal requirement.

Want the same math on a real layout? Load a worked example next and watch the live estimate change.

Want a worked example you can load?

Pick an example to see how wall count, openings, and waste change the live estimate.

These are illustrative planning examples, not customer projects.

20 × 8 ft straight wall

One straight wall shows the baseline nominal-module estimate.

Inputs

  • Wall 1: 20 × 8 ft
  • 8×8×16 Standard nominal block; 10% project waste.

Result: 180 base + 18 waste = 198 blocks to buy.

Why this result, and what it skips
Why this result?
160 sq ft net area becomes 180 whole base blocks; project waste applies once after that.
What to buy from it
Treat the order total as a starting quantity to confirm with your supplier.
Rule to reuse
Enter length and height for a plain rectangular wall, then set project waste.
What it does not cover
Does not choose a footing, reinforcement, or structural wall detail.

24 × 8 ft wall with a garage opening

A garage wall subtracts one wide opening before the block count is rounded.

Inputs

  • Wall 1: 24 × 8 ft
    • Door opening: 9 × 7 ft
  • 8×8×16 Standard nominal block; 10% project waste.

Result: 146 base + 15 waste = 161 blocks to buy.

Why this result, and what it skips
Why this result?
The 63 sq ft opening comes out of gross area before rounding and saves 70 base blocks.
What to buy from it
Skip blocks for the opening; keep waste for cuts and breakage.
Rule to reuse
Add every door or window to its wall, then check the rounded whole-block effect.
What it does not cover
Does not design a garage lintel, reinforcement, footing, or opening support.

Three-wall project

Three differently sized walls share one project total instead of separate one-wall orders.

Inputs

  • Wall 1: 20 × 8 ft
  • Wall 2: 16 × 8 ft
  • Wall 3: 12 × 6 ft
  • 8×8×16 Standard nominal block; 10% project waste.

Result: 405 base + 41 waste = 446 blocks to buy.

Why this result, and what it skips
Why this result?
Each of the 3 walls rounds to whole base blocks first; one project waste covers the combined total.
What to buy from it
One combined order total can simplify supplier talk while each wall stays visible for a field check.
Rule to reuse
Enter each rectangular wall separately so dimensions and openings stay on the right wall.
What it does not cover
Does not plan pallet loading, delivery, structural design, or site sequencing.

These scenarios estimate ordinary rectangular CMU wall materials only. They do not size lintels, reinforcement, or footings; plan delivery or pallet quantities; or provide structural design.

Need coverage by block size next? The nominal module table is below.

Which nominal CMU size covers how much wall?

Presets use the nominal face module, not the smaller specified unit. A standard 8 x 8 x 16 in face covers about 0.89 sq ft, the same as 1.125 blocks per sq ft, or 12.5 blocks per square meter for a 400 x 200 mm face.

  • Do not add the mortar joint a second time.
  • Specified CMU size is typically 3/8 in smaller than nominal so the mortar joint fits the layout module.
Nominal sizeBlocks / sq ftPlanning use
4 x 8 x 16 in1.125Partitions and veneer layouts
6 x 8 x 16 in1.125Thinner CMU wall layouts
8 x 8 x 16 in1.125Common CMU wall module
10 x 8 x 16 in1.125Wider CMU wall layouts
12 x 8 x 16 in1.125Wider CMU wall layouts

Where do these estimate assumptions come from?

Last reviewed August 2026

Each source note states the assumption it supports. Confirm local unit dimensions, packaging, and product yield with your supplier before ordering.

CMHA CMU-TEC-001

Supports typical nominal CMU modules and specified dimensions that are commonly 3/8 in smaller.

QUIKRETE Mortar Mix data sheet

Lists up to 13 standard 8 x 8 x 16 blocks per 80-lb bag. Homepage planning uses a 60-lb premix basis of 9 standard blocks per bag, conservatively below that published coverage. It does not establish a universal yield for 60-lb products.

Is this a material estimate or structural approval?

  • Estimates blocks and auxiliary mortar for ordinary rectangular CMU walls, including foundation wall and garage wall layouts entered by length and height.
  • Does not design rebar, bond beams, lintels, footings, or reinforcement.
  • Does not check building code, permits, structural capacity, or engineering approval, and it is not a contractor bid.

Who maintains the method, and when is it reviewed?

The site operator maintains the calculator method, sources, result labels, scenarios, limitations, and user guidance.

We update the review date when a formula, source, result label, example, limitation, or user guidance changes. Cosmetic wording or layout edits do not refresh the date.

Need mortar, fill, retaining walls, or installed cost?

This page counts standard wall blocks. Open a dedicated calculator when the material or method changes.

Joint mortar

Estimate whole 80-lb or 60-lb mortar bags with editable product coverage and an order buffer.

Open mortar calculator

Core fill or grout

Estimate grout volume for selected CMU cells instead of treating fill as wall block count.

Open fill calculator

Retaining wall materials

Count landscape blocks, caps, base gravel, and drainage backfill with retaining-wall formulas.

Open retaining wall calculator

Installed wall cost

Estimate blocks, mortar, optional grout, labor, and editable regional planning costs.

Open wall cost calculator

Block weight, pallet loading, transport, and curved or irregular walls are not calculated here. No empty estimate is provided for those tasks.

Questions before you order

How many blocks do I need for a 1,000 square foot wall?
For a 16 x 8 in nominal face, use 1.125 blocks per sq ft. A 1,000 sq ft net wall is 1,125 base blocks before waste. If that area still includes doors or windows, subtract those openings first, then apply waste once.
What if the wall is not a whole number of blocks long?
Each wall rounds up to whole blocks from the nominal face module. A leftover strip still counts as a full block in that direction. Treat that as a purchase check, not a cut list or bond layout.
Does this work as a cinder block calculator or CMU block calculator?
Yes, when those terms mean ordinary rectangular concrete masonry units, including standard hollow CMU. Pick the right nominal module and confirm the product with your supplier. AAC, glass block, curved walls, and specialty systems stay outside this calculator.
Does this calculator cover retaining walls or structural design?
No. Use the retaining wall calculator for landscape blocks, caps, gravel, and backfill. Rebar, lintels, code, permits, and structural approval need project documents and qualified local professionals.
Is the cost result a contractor bid?
No. Optional homepage pricing covers block and mortar materials only. It excludes labor, footings, permits, reinforcement, waterproofing, delivery, and other installed-cost items.