Calculated result
173blocks
Blocks to order
Formula
MAS-CMU-001(wall length × height − openings) ÷ (nominal face length × height) × (1 + waste)
139 ft²
Net wall area
0.889 ft²
Nominal face area
156.4 blocks
Mathematical quantity
Masonry calculator
Concrete block calculator
CMU count and mortar-bag planning from wall area, opening deductions and nominal block face size.
By Feroz Sheikh · Formula MAS-CMU-001 v1.0.0 · Tested formula
Formula
MAS-CMU-001v1.0.0Project inputs
Enter your measurements. Switching units converts the same project, including coverage and unit rates. Package yields keep the unit printed beside each field.
Refine measurements and rates at any time. Your current values are included in the material-list PDF.
Planning estimate, not engineering advice. Confirm site measurements and product specifications. Calculation limits.
This calculator counts CMU and mortar bags from net wall area, openings and a nominal face that already includes the joint. Formula MAS-CMU-001 v1.0.0. Waste stays visible. Drop the count into an estimate. Corners, lintels and grout fill stay companion lines.
- Measure finished wall length and height.
- Deduct actual door and window openings.
- Use the nominal block face that matches the selected unit, then confirm mortar yield on the bag.
Size chart
CMU wall chart (16×8 in face, one door, 10% waste)
Nominal face already includes the mortar joint. Lintels stay extras.
| Wall | Primary | Check |
|---|---|---|
| 10 × 8 ft | 74 blocks | 59 ft² |
| 20 × 8 ft | 173 blocks | 139 ft² |
| 30 × 8 ft | 272 blocks | 219 ft² |
| 40 × 8 ft | 333 blocks | 269 ft² |
Metric example — 6 × 2.4 m wall. A 6 × 2.4 m wall with 10% waste returns 192 blocks. Nominal face still includes the joint.
- NCMA. Nominal CMU face includes the mortar joint. This count is a takeoff, not a wall design. NCMA — concrete masonry unit sizes
Add your project costs
Enter supplier prices and any labour, equipment or delivery costs. Pick a currency — badges, inputs, and totals follow.
Costs use the block, brick or mortar rate you type. Construclytic does not fetch masonry prices. Lintels, corners and labour stay separate estimate lines. For GCC projects, select QAR, AED, SAR, KWD, OMR or BHD and enter local supplier rates.
How this calculator works
A transparent concrete block calculator takeoff.
Feroz SheikhWritten by Feroz Sheikh · founder
This calculator divides net wall area by the selected nominal CMU face, which already includes the mortar joint, then rounds whole blocks and mortar bags after a visible allowance.
CMU counts use nominal face size that already includes the mortar joint. If you use actual unit size and then add joint thickness again, you double-count the joint. Openings deduct after net wall area.
Worked example. Example: a 20 ft × 8 ft wall with one 21 ft² door has 139 ft² of net area. Standard 8 × 16 in nominal blocks cover 0.889 ft² each, so 173 blocks are purchased after 10% waste and 6 mortar bags at 33 blocks per bag.
See the example inputs and calculated result
This separate example uses the calculator's starting values in imperial units. It stays unchanged when you edit the tool above. Example rates, yields and dimensions are assumptions, not recommendations for your project.
| Input | Example value |
|---|---|
| Wall length | 20 ft |
| Wall height | 8 ft |
| Nominal block length | 16 in |
| Nominal block height | 8 in |
| Doors | 1 count |
| Windows | 0 count |
| Door deduction | 21 ft² |
| Window deduction | 15 ft² |
| Blocks per mortar bag | 33 blocks / bag |
| Waste factor | 10 % |
Example result: Blocks to order — 173 blocks.
(wall length × height − openings) ÷ (nominal face length × height) × (1 + waste)
Use the labelled units above when reproducing this example. To work in metric, switch the calculator to Metric; applicable measurements are converted, while product-specific units remain labelled.
- 1. Measure finished wall length and height.
- 2. Deduct actual door and window openings.
- 3. Use the nominal block face that matches the selected unit, then confirm mortar yield on the bag.
Field notes that change the number
- An 8×16 nominal face is the usual 0.89 ft² planning unit.
- Bond beams, lintels and grout fill are companion takeoffs.
- Cut waste is a percentage, not a second joint.
Common mistakes
- Using actual block size plus a 3/8 in joint on top of nominal face.
- Running brick and CMU through one calculator.
- Forgetting that a 20 ft² door is not always a full-block save.
Need the broader workflow? Read the masonry planning guide.
How-to: How to count CMU and brick
Questions
Questions about concrete block calculator
Does nominal size include mortar?
Yes. An 8 × 8 × 16 in nominal CMU is planned on an 8 × 16 in face that already includes a typical mortar joint.
Does this fill block cores?
No. Grout fill, bond beams, lintels and reinforcement are separate takeoffs.
How many concrete blocks for a 20x8 wall?
A 20 × 8 ft wall with one door, 16×8 in nominal face and 10% waste returns 173 blocks. Nominal size already includes the joint.
Does nominal block size include mortar?
Yes. An 8×8×16 CMU is planned on a 16×8 in face that already includes the mortar joint.
What is the formula ID?
This concrete block calculator publishes formula MAS-CMU-001, version 1.0.0. The ID stays on the result and on the estimate line.