Free Calculator · Published November 2026
Concrete Block Calculator for a Nominal 8 by 16 Face
A concrete block calculator counts units from wall length and height. The face used here is the nominal 8 inch by 16 inch module. A 20 foot wall that is 8 feet tall is 180 blocks before waste and before openings. The specified block is smaller than that module.
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Inches of length divided by 16, times inches of height divided by 8. Waste is a percent you type. Openings come off in the same nominal square inches.
The count uses the nominal 8 by 16 inch face. Specified size is typically 3/8 inch less. Leave bags and grout blank unless you have a yield.
180.000 blocks on the nominal grid is 180.000 net. Waste is 0, so the order count matches the net.
All calculations are estimates based on historical information and should be verified by the user.
Important: nominal is the module, not the measured unit
All calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.
Nominal Face, Specified Block
The CMHA document on concrete masonry unit shapes and sizes, fetched the day this page was written, says concrete masonry units typically have a nominal face of 8 inches high by 16 inches long. Nominal dimensions are the module for bond patterns and for door and window layout. Specified dimensions are typically 3/8 inch less than nominal dimensions, so that module is held with a 3/8 inch mortar joint. The figure for a nominal 8 by 8 by 16 inch unit shows 7 5/8 inch and 15 5/8 inch. This concrete block calculator counts on the nominal face. Measuring the bare unit and dividing by 15 5/8 would drop the joint and mis-count the wall.
What the fetch actually printed
| Item | From the CMHA fetch |
|---|---|
| Nominal face | Typically 8 in high by 16 in long |
| Specified versus nominal | Typically 3/8 in less |
| Figure on an 8 × 8 × 16 | 7 5/8 in and 15 5/8 in |
| ASTM C90 tolerance, as described | No more than ±1/8 in from specified dimensions |
| Mortar bags and core volume | Not printed. Boxes stay blank. |
Worked wall
Length 20 feet is 240 inches. 240 ÷ 16 = 15 blocks along the wall. Height 8 feet is 96 inches. 96 ÷ 8 = 12 courses. 15 × 12 = 180 blocks with waste at zero and no opening. Five percent waste is 189 blocks. An opening is subtracted as square feet times 144, divided by 128, because the nominal face is 16 by 8 inches. That subtraction is geometry. It is not a claim about how a mason cuts a jamb.
How should the block order read?
- Wall length and height, and that the count used the nominal 8 by 16 face.
- Openings in square feet, or a note that openings were zero.
- Waste percent you typed. Zero stays zero.
- Blocks per bag only if the bag itself printed a yield. Otherwise leave bags off.
- Grout only if you typed cubic feet per block. No core volume was fetched.
- A line that poured yards are a different tool.
Poured concrete is not this count
Cubic yards of a slab, a footing, or a column stay on the concrete calculator. This page does not turn a block wall into ready-mix. Volume with no unit count is the cubic yard calculator. Half-length units, bond beams, and corner returns are not in the 8 by 16 grid. Add those from the supplier's shape sheet. The CMHA text says local producers can make other heights and lengths. Check that sheet before you treat 180 as the pallet.
Why the Joint Is Part of the Count
A nominal 8 by 16 inch face is a module, not the block you hold. The CMHA text says specified dimensions are typically 3/8 inch less, so the mortar joint restores the module. The figure on a nominal 8 by 8 by 16 unit shows 7 5/8 inch and 15 5/8 inch. If you divide the wall by 15 5/8, you are counting bare units as if they touched. They do not. The count on this page divides by 16 and by 8 on purpose.
ASTM C90, as that same document describes it, allows overall width, height, and length to vary by no more than 1/8 inch from the specified dimensions. Split-face and slump faces are called out as exceptions because the texture is meant to be uneven. A tolerance is not a second module. Do not add 1/8 inch into the divisor. Order the nominal count, then let the supplier's actual run confirm the corners.
Openings are square feet you type. The subtraction is opening square feet times 144, divided by 128, because 16 times 8 is 128 square inches. A door that is not a clean multiple of the module still needs a cut block. This page does not add the half-length units the CMHA text says an all-purpose unit can be split into. Add those from the shape sheet. Bond beams, sashes, and corners are the same omission. They are real pieces. They were not given a count formula on the fetch.
Mortar bags and core fill stay blank until you type a yield. No blocks-per-bag figure and no cubic feet of grout per core were in the CMHA fetch, so a default would be an invention. Waste is a percent you type. Zero means the order matches the net count. Five percent on the 20 by 8 foot example is 189 blocks, which is 180 times 1.05. That five is an illustration of the box, not a recommended waste factor.
Frequently Asked Questions
How does the count use the nominal face?
It divides wall length in inches by 16 and wall height in inches by 8, using the nominal 8 by 16 inch face. A 20 foot by 8 foot wall is 15 blocks along and 12 courses, which is 180 blocks. The specified unit is smaller. The mortar joint is what makes the nominal module.
What is nominal versus actual on a concrete block?
The CMHA document fetched for this page says specified dimensions are typically 3/8 inch less than nominal dimensions, so a 3/8 inch mortar joint holds an 8 inch module. The figure for a nominal 8 by 8 by 16 unit shows 7 5/8 inch and 15 5/8 inch. ASTM C90, as that document describes it, allows overall dimensions to vary by no more than 1/8 inch from the specified dimensions.
Does the count include mortar bags?
Only if you type how many blocks one bag covers. No bag yield was on the CMHA fetch, so the box starts empty and the bag line stays blank. The same is true for core fill: type cubic feet of grout per block or leave it blank.
Is this the poured concrete calculator?
No. The concrete calculator is cubic yards of poured concrete. This concrete block calculator counts concrete masonry units on a nominal 8 by 16 face. It does not convert the wall into ready-mix yards.
Save the Block Count
The nominal count, the waste you typed, and any opening belong on the job record.
Get a Free DemoAll calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.