Cinder Block Calculator
Enter your wall’s length, height, and openings to find out how many cinder blocks and mortar bags you need. The calculator works for 6, 8, and 12 inch standard block.
Total area of doors, windows or other openings to subtract.
Covers cuts, breakage and layout waste. 5–10% is normal.
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Ordering tips
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Coverage & waste
Material profile
For a 24 ft × 8 ft wall (192 sq ft) with 21 sq ft of openings, you need 171 sq ft of net block coverage. Using standard 8×8×16 in block at 0.89 sq ft each, that comes to 212 blocks with a 10% waste allowance, plus 7 mortar bags — about $469.00 total at $1.75 per block and $14 per mortar bag.
How many blocks do common wall sizes need?
These figures use standard 8×8×16 in block (0.89 sq ft face each) and a 10% waste allowance.
| Wall size | Openings | Units needed | Mortar bags |
|---|---|---|---|
| 10 ft × 4 ft | 0 sq ft | 50 blocks | 2 bags |
| 20 ft × 6 ft | 8 sq ft | 139 blocks | 5 bags |
| 30 ft × 8 ft | 24 sq ft | 267 blocks | 9 bags |
| 40 ft × 8 ft | 30 sq ft | 359 blocks | 11 bags |
| 50 ft × 10 ft | 40 sq ft | 569 blocks | 18 bags |
| 60 ft × 8 ft | 45 sq ft | 538 blocks | 17 bags |
Cinder block sizes and uses
| Type | Coverage / unit | Size | Best for |
|---|---|---|---|
| 8in standard block (8 x 8 x 16in) | 0.89 sq ft | 8 x 8 x 16in | Foundation & load-bearing walls |
| 6in block (6 x 8 x 16in) | 0.89 sq ft | 6 x 8 x 16in | Non-load-bearing partition walls |
| 12in block (12 x 8 x 16in) | 0.89 sq ft | 12 x 8 x 16in | Heavy load-bearing / retaining |
How to calculate how many cinder blocks you need
- Measure the wall Multiply length by height in feet to get gross wall area.
- Subtract openings Deduct the square footage of doors, windows, and any other unblocked openings.
- Add your waste allowance Multiply net area by 1 plus your waste percentage (10% is typical) to cover cuts and breakage.
- Divide by coverage per block Every standard block face — 6, 8, or 12 in thick — covers about 0.89 sq ft; divide net area by this and round up.
- Calculate mortar bags Divide the block count by roughly 33 blocks per 80 lb mortar bag and round up.
Worked example
Here’s the math for a 24 ft × 8 ft wall with 21 sq ft of openings using standard 8×8×16 in block.
- Wall length × height24 ft × 8 ft = 192 sq ft
- Openings deducted21 sq ft
- Net block area171 sq ft
- Area with 10% waste188.1 sq ft
- Blocks needed (0.89 sq ft each, 8×8×16)212 blocks
- Mortar bags (1 per 33 blocks)7 bags
- Estimated material cost212 × $1.75 + 7 × $14 = $469.00
Typical wall sizes and block quantities
| Wall size | Net area | Quantity needed |
|---|---|---|
| Small retaining wall (15×3 ft) | 45 sq ft | 56 blocks |
| Garden shed foundation wall (20×4 ft) | 80 sq ft | 99 blocks |
| Property line wall (40×6 ft) | 240 sq ft | 297 blocks |
| Garage wall (24×8 ft, door opening) | 174 sq ft | 216 blocks |
| Basement foundation wall (60×8 ft, opening) | 465 sq ft | 575 blocks |
Ordering block by the pallet/cube
Cinder blocks are typically sold in cubes of around 90 to 100 blocks per pallet, depending on thickness. Ordering by the full cube usually gets a better per-block price than buying individually, and most suppliers deliver pallets directly to the job site with a forklift. Always add a few extra blocks for cuts and breakage beyond your calculated total.
- Small jobs (under 100 blocks)Buying individually or a single cube is usually enough
- Medium jobs (100–500 blocks)Order by the cube and compare per-block pricing against individual purchase
- Large jobs (500+ blocks)Coordinate delivery in multiple cubes and confirm site access for pallet drop-off
Common mistakes
- Not deducting door and window openingsOpenings reduce the net area that actually needs block
- Choosing the wrong block thickness6 in block isn’t rated for load-bearing walls; 8 in or 12 in is needed for foundations and retaining walls
- Forgetting rebar and grout for structural wallsBlock count alone doesn’t cover vertical rebar and core-fill grout required in load-bearing or retaining walls
- Underestimating waste for cuts at cornersCorner blocks, half-blocks, and control joints use more units than a straight running-bond wall
- Miscounting coursesStandard 8 in block plus a 3/8 in joint runs 1.33 courses per foot of wall height — a common source of undercounting
- Skipping the mortar allowanceBlock count and mortar bags are separate line items — don’t forget to order both
What this calculator assumes
Adjust your result if your project differs from these.
- Coverage per block (0.89 sq ft) is based on a standard 8×16 in face with a 3/8 in mortar joint, and applies to 6, 8, and 12 in thicknesses equally since face size is the same.
- Openings for doors, windows, and vents are subtracted from gross wall area before waste is applied.
- The default 10% waste allowance covers cuts, breakage, and corner returns.
- Mortar bags are estimated at roughly 1 per 33 blocks based on an 80 lb bag.
- Block and mortar counts are rounded up to the nearest whole unit.
- This calculator estimates block and mortar only — rebar, grout, and footing materials are calculated separately.
Common questions
How many blocks per square foot of wall?
Standard block needs about 1.12 blocks per sq ft (1 ÷ 0.89), including a standard mortar joint.
Does block thickness change how many I need?
No — 6, 8, and 12 in blocks all have the same 8×16 in face, so the block count per sq ft stays the same. Thickness affects strength and cost per block, not quantity.
How much mortar do I need per block?
Roughly 1 mortar bag covers 33 blocks for standard 3/8 in joints.
How many blocks come on a pallet?
Cinder blocks typically ship in cubes of around 90 to 100 blocks per pallet.
Should I deduct openings for doors and windows?
Yes. Subtract the total square footage of all openings from your gross wall area before calculating block count.
How much waste should I add for cinder block?
10% is standard for straightforward walls. Increase to 15% for walls with lots of corners, control joints, or half-block cuts.
How many blocks are in a course (row)?
A standard 16 in long block means about 0.75 blocks per linear foot, so a 24 ft wall needs 18 blocks per course.
Do I need rebar and grout in addition to block and mortar?
Yes, for load-bearing or retaining walls. Vertical rebar and core-fill grout are calculated separately from the block and mortar count.
What's the difference between cinder block and CMU?
“Cinder block” is the common name for concrete masonry units (CMU); older cinder block used coal cinders as aggregate, while modern CMU uses concrete aggregate.
How much does a cinder block wall cost per square foot?
At $1.75 per block and about 1.12 blocks per sq ft, material alone runs roughly $1.96 per sq ft before mortar, rebar, and labor.
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Project
| Wall size | — |
| Openings deducted | — |
| Net area | — |
| Material | — |
| Waste allowance | — |
Shopping list
| Units needed | — |
| Mortar / mix | — |
| Estimated total cost | — |
Notes
Estimate generated by materialcalculate.com. Confirm quantities with your supplier before ordering.