Concrete Block Calculator
Count concrete blocks (CMU) for a wall — blocks, mortar bags, core-fill grout, and reinforcement — for all standard block sizes. Includes a fill-option comparison and a downloadable PDF material list.
Counts use nominal block sizes with mortar joints. Mortar and grout yields vary with joint size, mix, and technique — order a little extra. For planning purposes only.
| Fill Option | Grout (cu yd) | Rebar (ft) | Added Cost | Total |
|---|
Blocks + mortar are the same for every option; only grout & rebar change. For your 8" block wall.
How to use the concrete block calculator
Four quick steps turn your wall dimensions into a full CMU material list — blocks, mortar bags, core-fill grout, rebar, and a cost breakdown — for any standard block size.
Enter the wall size
Length × height in feet, any door/window openings to subtract, and how many identical walls — or tap a preset like 20×8 wall.
Pick block & core fill
Choose a block size from 4″ to 12″ (or half-high), then set core fill to none, rebar cells at a spacing, or full cores.
Set waste & prices
Allow 5–10% for cuts and breakage, and enter block, mortar, grout, and rebar prices for a live cost estimate.
Read results & save a PDF
Get block count, mortar bags, courses, grout, rebar, a fill-option comparison, and a downloadable PDF material list.
How the block count is calculated
Block counting starts from wall area and the block’s face size. Everything else — mortar, courses, grout, rebar — follows from the block count and your fill choice. Here is the exact math behind each output.
Worked example — a 20 ft × 8 ft standard 8″ block wall
Face area: 20 × 8 = 160 sq ft
Raw blocks: 160 × 1.125 = 180
With 5% waste: 180 × 1.05 = 189 blocks
Mortar: 189 ÷ 13.5 = 14 bags | Courses: 96 ÷ 8 = 12
≈ 189 blocks, 14 bags of mortar, 12 courses of 15 block each.
Block estimating charts
Handy lookups for the most common block questions — blocks by wall area, standard block sizes, core-fill grout, and typical jobs. Figures use nominal sizes with mortar joints, so add 5–10% for cuts and breakage.
| Net wall area | Blocks (no waste) | + 5% waste | + 10% waste |
|---|---|---|---|
| 100 sq ft | 113 | 119 | 124 |
| 200 sq ft | 225 | 237 | 248 |
| 300 sq ft | 338 | 355 | 372 |
| 500 sq ft | 563 | 591 | 619 |
| 1000 sq ft | 1,125 | 1,182 | 1,238 |
Based on 1.125 block per sq ft. Half-high (4″-tall) block doubles every figure. All standard widths (4″–12″) share the same 16×8 face, so the block count is identical — only grout and cost change with width.
| Block | Blocks / sq ft | Course height | Full-core grout | Typical use |
|---|---|---|---|---|
| 4″ (4×8×16) | 1.125 | 8 in | 0.10 ft³/sq ft | Partitions, veneer |
| 6″ (6×8×16) | 1.125 | 8 in | 0.18 ft³/sq ft | Light walls, fences |
| 8″ (8×8×16) | 1.125 | 8 in | 0.27 ft³/sq ft | Standard foundation/wall |
| 10″ (10×8×16) | 1.125 | 8 in | 0.34 ft³/sq ft | Taller, loaded walls |
| 12″ (12×8×16) | 1.125 | 8 in | 0.40 ft³/sq ft | Tall / retaining walls |
| 8″ half-high (8×4×16) | 2.25 | 4 in | 0.27 ft³/sq ft | Accent, coursing |
Full-core grout is the volume to fill every cell. Reinforced-cell fill (rebar cells only) uses far less — the calculator works it out from your cell spacing.
| Block width | Grout per sq ft | Per 100 sq ft (cu ft) | Per 100 sq ft (cu yd) |
|---|---|---|---|
| 6 in | 0.18 ft³ | 18 ft³ | 0.67 yd³ |
| 8 in | 0.27 ft³ | 27 ft³ | 1.00 yd³ |
| 10 in | 0.34 ft³ | 34 ft³ | 1.26 yd³ |
| 12 in | 0.40 ft³ | 40 ft³ | 1.48 yd³ |
Only applies when you fill every core. Most structural walls grout just the reinforced cells, using a fraction of these amounts. 1 cubic yard = 27 cubic feet.
| Job | Dimensions | Block | Blocks (+5%) | Mortar bags |
|---|---|---|---|---|
| Garden / fence wall | 50 × 6 ft | 6″ | 355 | 27 bags |
| Small building wall | 20 × 8 ft | 8″ | 189 | 14 bags |
| Garage perimeter (one side) | 40 × 8 ft | 8″ | 378 | 28 bags |
| Tall wall | 30 × 10 ft | 8″ | 355 | 27 bags |
| Retaining wall | 100 × 4 ft | 12″ | 473 | 36 bags |
Blocks at 1.125/sq ft + 5% waste; mortar at ~13.5 block per 80 lb bag. Add grout and rebar separately if cores are filled. Bag and block counts are rounded up.
Everything the calculator works out
One set of wall dimensions gives you a complete CMU order — every count a mason or supplier needs, plus a costed fill comparison.
Key figures every block wall depends on
Built for any block wall
From a low garden wall to a full structural build, the same calculator scales to the job.
Laying a garden, fence, or low retaining wall and wants an exact block and mortar order without over-buying.
- Start from a preset like Fence 50×6
- Pick a 4–6″ block for light walls
- Subtract gates and openings
Building foundation, garage, or load-bearing block walls and needs blocks, mortar, grout, and rebar for a bid.
- Batch identical walls by quantity
- Compare none / cells / full fill cost
- Keep the PDF on file for quotes
Scoping a build with several block walls of different sizes rolled into one materials budget.
- Model each wall size separately
- Total blocks for pallet ordering
- Use the fill table to price options
7 tips for an accurate block order
Small habits keep your count right the first time and your wall straight, plumb, and on-module.
Concrete block calculator FAQ
The counts, coverage rates, and ordering questions people ask most before laying a block wall.
Multiply the wall area (length × height in feet, minus openings) by the blocks per square foot, then add waste. A standard 8×8×16 block covers about 1.125 blocks per square foot.
Example: a 20 × 8 ft wall = 160 sq ft × 1.125 = 180 blocks, or about 189 with 5% waste. Half-high (4″) block doubles the count to 2.25 per square foot.
A standard block has a nominal 16 × 8 inch face — about 0.89 sq ft — so it takes roughly 1.125 blocks to cover one square foot of wall. Half-high (16 × 4 inch) block covers half as much, so you need about 2.25 per square foot.
Multiply your net wall area by these figures to get a raw block count before adding waste.
A standard 80 lb bag of Type S or N mortar lays roughly 13 to 15 blocks, so about 13.5 on average. Divide your block count by 13.5 and round up.
A 180-block wall needs about 14 bags. Joint size, block texture, and how full you butter the joints all shift the real number, so keep a spare bag or two on hand.
It depends on whether you fill every core or only the reinforced cells. Filling all cores of an 8″ wall takes about 0.27 cu ft per square foot — roughly one cubic yard per 100 sq ft. Filling only rebar cells at, say, 48″ on center uses a fraction of that.
Grout is ordered in cubic yards (27 cu ft each) or mixed from bags for small jobs.
Block width is a structural choice. As a guide, 4 and 6 inch block suit partitions, veneers, and light garden walls; 8 inch is the standard for most foundation and structural walls; and 10 to 12 inch is used for tall, heavily loaded, or retaining walls.
Confirm the size, reinforcement, and footing with your engineer and local code before ordering.
A course is one horizontal row. With 16-inch-long block, each course needs about (wall length in inches ÷ 16) blocks — 15 for a 20 ft wall. Standard block is 8 inches high, so courses = wall height in inches ÷ 8, which is twelve courses for an 8 ft wall.
Half-high block is 4 inches tall, so it doubles the number of courses.
Most structural block walls are reinforced with vertical rebar in grouted cells, often 32 to 48 inches on center, plus horizontal bond-beam or joint reinforcement. Retaining and tall walls need more.
Bar size, spacing, and grouting are structural decisions — always follow your engineer’s design and local code rather than a rule of thumb.
Add about 5 to 10 percent for breakage, cuts around openings, and corners. Odd-shaped walls and lots of openings push toward the higher end.
Blocks usually ship by the pallet and suppliers rarely break a bundle, so round up to whole pallets where you can — returning a few blocks beats stopping a lay halfway.
General Estimating Notice: This calculator counts blocks using nominal sizes with standard mortar joints and provides mortar, grout, rebar, and cost estimates from typical material yields. Actual quantities vary with joint size, mix, block maker, and technique, so order a little extra rather than running short. Block size, core-fill pattern, and reinforcement are structural decisions — verify them with your local building code and engineer before ordering. For planning purposes only.