Concrete block calculator
Concrete block calculator: how many cinder blocks do you need?
Divide the wall’s area by one block’s face. A standard concrete block is 16 by 8 inches nominal, so a square foot takes 1.125 blocks: a 40 foot wall 6 feet high is 240 square feet, or 270 blocks before waste. Enter your wall below, take off doors and windows, and the calculator gives blocks, courses and cost. Standard block sizes, nominal and actual, are in the table further down.
How many blocks you need
240 sq ft of wall. Courses and blocks per course are for a plain wall with no openings; use “blocks to order” for the count.
Standard concrete block sizes
US blocks are named by nominal size, which includes a 3/8 inch mortar joint; the block itself is 3/8 inch smaller each way. Specialty and local blocks can differ, so check your supplier’s sizes.
| Called (W × H × L, in) | Actual block (in) | Blocks per sq ft of wall |
|---|---|---|
| 4 × 8 × 16 | 3-5/8 × 7-5/8 × 15-5/8 | 1.125 |
| 6 × 8 × 16 | 5-5/8 × 7-5/8 × 15-5/8 | 1.125 |
| 8 × 8 × 16 | 7-5/8 × 7-5/8 × 15-5/8 | 1.125 |
| 10 × 8 × 16 | 9-5/8 × 7-5/8 × 15-5/8 | 1.125 |
| 12 × 8 × 16 | 11-5/8 × 7-5/8 × 15-5/8 | 1.125 |
| 8 × 4 × 16 (half-high) | 7-5/8 × 3-5/8 × 15-5/8 | 2.25 |
| 8 × 8 × 8 (half block) | 7-5/8 × 7-5/8 × 7-5/8 | 2.25 |
The width (wall thickness) changes how thick the wall is, not how many blocks cover a square foot.
How to estimate block for a wall
- Measure the wall. Length and height in feet; multiply for square feet.
- Take off openings. Doors and windows, in square feet.
- Divide by the block face. Standard 16 × 8 blocks: 1.125 per square foot.
- Add extra for cuts at corners and openings, and for breakage.
- Check the courses. Wall height in inches ÷ 8 for standard block.
Pouring a footing for the wall? Use the concrete calculator. Gravel behind a retaining wall? The gravel calculator. A patio in front of it? The paver calculator.
Frequently asked questions
- How many concrete blocks do I need?
- Divide the wall's area by the area of one block's face. A standard block's face is 16 by 8 inches nominal, which is 128 square inches, so a square foot (144 square inches) takes 144 ÷ 128 = 1.125 blocks. A 40 foot wall 6 feet high is 240 square feet, or 240 × 1.125 = 270 blocks, before waste.
- How many cinder blocks are in a square foot?
- 1.125 standard blocks (16 by 8 inches nominal) cover one square foot. Half-high blocks (16 by 4) take 2.25 per square foot, and 8 by 8 faces take 2.25 as well.
- What size is a standard concrete block?
- In the US, the common block is called 8 × 8 × 16 inches. That is its nominal size, which includes a 3/8 inch mortar joint; the block itself measures 7-5/8 × 7-5/8 × 15-5/8 inches. Laid with 3/8 inch joints, each block takes up exactly 8 × 16 inches of wall.
- What is the difference between nominal and actual block size?
- Nominal size is the space a block takes up in the wall, mortar joint included; actual size is the block itself, 3/8 inch smaller in each dimension. Wall layouts and this calculator use nominal sizes.
- How many courses of block do I need?
- Divide the wall height by the block's nominal height: a 6 foot wall is 72 inches, which is 72 ÷ 8 = 9 courses of standard block.
- How much does a cinder block weigh?
- It depends on the size and on whether the block is lightweight or normal-weight, so there is no single figure. Your supplier lists the weight of the blocks they sell; that also tells you how many a truck or trailer can carry.
- How much mortar do I need for block?
- Mortar per block depends on the joint size, the block and how it is laid. The mortar bag's label or your supplier gives how many blocks a bag lays; use that with the block count from this calculator.
- Does this work for retaining wall blocks?
- Yes. Retaining wall blocks come in many face sizes, so choose 'Other size' and enter the face length and height from the manufacturer, and follow the manufacturer's installation guide for anything structural.
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