How this concrete block calculator works
A standard block (nominal 8 × 8 × 16 in) covers 0.89 ft² of wall including its mortar joints, so block count is wall area times 1.125. The calculator subtracts openings, applies the block trade's 5% waste convention, and figures mortar and core fill from published coverage:
mortar = blocks ÷ 13 per 80 lb bag · core fill = 0.84 yd³ per 100 blocks
At the defaults — a 20 × 8 ft wall — that’s 189 blocks and 15 mortar bags, about $473 in block and $109 in mortar; the line-by-line math is in the block math section below.
The parts of a block wall
A concrete-block wall is more than a stack of units — it’s a system of footing, block, mortar, steel and cap, and the calculator counts the visible layers while the rest gets budgeted alongside:
Footing
The poured base the wall stands on, typically twice the wall width and below frost depth. No block wall is stronger than its footing — size the pour with the footing calculator before you order a single block.
The block (CMU)
The units this tool counts: standard stretcher block for the field, plus corner, half, bond-beam and cap units for the details. Nominal 8 × 8 × 16 in (actually 7⅝ each way, the ⅜ in of mortar making up the “nominal” inch).
Mortar joints
The ⅜ in beds and head joints that bond the units and carry the wall’s tolerance — 13 blocks per 80 lb bag is the planning figure. Type S below grade, type N above is the common split.
Reinforcement and core fill
Vertical rebar in grouted cells and horizontal joint reinforcement or bond beams tie the wall against wind and earth pressure. Grout fills only the reinforced cells on most walls — the calculator’s fill-all-cores figure is the ceiling, not the order.
Bond beam and cap
A grouted, reinforced bond-beam course near the top ties everything together and spreads top loads; a solid cap block or poured cap closes the wall against water. Both are counted by the course from the drawings, on top of the field block.
Block types, mortar types and prices
“Concrete block” covers a family of units and two mortar types — order the right ones and the wall goes together without cutting:
- Stretcher block: the two-core field unit with flanged ends for the head joint — the bulk of any order and what this calculator counts.
- Corner / end block: one flat end for a finished corner or jamb; a handful per wall.
- Bond-beam & lintel block: channel-shaped units that hold horizontal rebar and grout over openings and at the top course.
- Half & cap block: half-length units to keep the running bond, and solid caps to close the top.
- Type S mortar below grade and for structural walls; type N above grade for general use — sold as 80 lb bags of pre-blended mix.
| Item | Typical range |
|---|---|
| Standard 8″ CMU | $2–4 / block |
| Corner / bond-beam block | $3–6 / block |
| Mortar mix, 80 lb | $6–9 / bag |
| Grout / core fill, per yd³ | $150–180 |
| #4 rebar, per 20 ft | $8–14 |
How many concrete blocks do I need?
Multiply wall square footage by 1.125 — or read the common wall sizes straight from the engine:
| Wall | Blocks | Mortar bags (80 lb) | Fill all cores |
|---|---|---|---|
| 10 × 4 ft | 48 | 4 | 0.38 yd³ |
| 20 × 4 ft | 95 | 8 | 0.76 yd³ |
| 20 × 6 ft | 142 | 11 | 1.13 yd³ |
| 20 × 8 ft | 189 | 15 | 1.51 yd³ |
| 30 × 8 ft | 284 | 22 | 2.27 yd³ |
| 40 × 8 ft | 378 | 30 | 3.02 yd³ |
How to measure a wall for block
Wall area minus openings drives the count; courses and per-course blocks help you sanity- check the stack. Dimension fields take feet-inches and metric.
- Measure the wall length and height. Height in courses is height ÷ 8 in — the calculator reports it, and it should land on a whole course.
- Subtract openings. Total the door and window areas in square feet and enter them; the engine takes them off before counting.
- Sanity-check per course: block per course is wall length ÷ 16 in (0.75 × length in feet). The default 20 ft wall is 15 blocks a course, 12 courses high.
- Leave waste at 5% — the masonry convention for breakage and cuts; raise it on walls with lots of corners and openings.
- Decide the grout separately. The fill-all-cores figure is the maximum; count only the reinforced cells your drawings call for.
- Enter block and mortar prices from your yard — and remember the footing, rebar and grout are their own orders.
Worked example: blocks for a 20 × 8 wall
The default wall, worked line by line — 20 × 8 ft, no openings, 5% waste, $2.50 block over $7.25 mortar:
blocks = 160 × 1.125 = 180 exact (12 courses × 15)
+ 5% waste = 189 → 189 blocks
mortar = 189 ÷ 13 = 14.5 → 15 bags
fill all cores = 180 × 0.84 ÷ 100 = 1.51 yd³
cost = 189 × $2.50 + 15 × $7.25 = $473 + $109 = $582
The exact 180 is a clean 12 courses of 15 — proof the wall lands on whole blocks, no partial course. The 9 blocks that 5% waste adds aren’t padding: corner cuts, the odd broken unit off the pallet, and the half-blocks that keep the running bond all come out of that margin. And note the core-fill line is the all-cores maximum — a wall reinforced every 32 in uses well under half of it.
What this block estimate doesn’t include
The calculator prices field block and its mortar. A finished wall carries more:
- Footing. The poured base under the wall — a separate concrete order.
- Rebar and grout. Vertical steel, joint reinforcement, and the grout for the reinforced cells and bond beam.
- Specialty units. Corner, bond-beam, lintel and cap block beyond the field stretchers.
- Waterproofing and drainage. Below-grade coating, drainage board and footing drain on foundation and retaining walls.
- Anchors and ties. Sill plates, anchor bolts, brick ties or veneer anchors as the design needs.
- Labor. The mason’s time is most of the bill — installed block runs $15–35 per ft², block included.
- Engineering and permits. Retaining walls and tall freestanding walls need a design and a permit.
Concrete block FAQ
How many concrete blocks do I need for 100 square feet?
About 113 standard 8 × 8 × 16 blocks before waste — each block covers 0.89 ft² of wall, so multiply wall area by 1.125. With the usual 5% waste for breakage and cuts, order 119. The calculator subtracts door and window openings before counting.
How many blocks does a bag of mortar lay?
About 13 standard blocks per 80 lb bag of mortar mix, per Quikrete’s published coverage. The default 20 × 8 ft wall (189 blocks with waste) needs 15 bags. Mix in small batches — mortar that sits more than an hour or two is wasted.
How many concrete blocks are on a pallet?
Usually 90 to 120 standard 8 × 8 × 16 blocks per pallet, depending on the yard and the block weight — figure a round 100 for planning. The default wall is close to two pallets. Order full pallets where you can; broken-pallet pricing and loose handling cost more.
How much grout does it take to fill block cores?
Filling every core of standard 8 in block takes about 0.84 yd³ of grout per 100 blocks — the default 20 × 8 wall runs 1.51 yd³. Most walls only grout the reinforced cells (commonly every 24–48 in plus corners), so the real number is a fraction of that; your design drawings govern.
What is a bond beam?
A horizontal reinforced course near the top of a block wall (and sometimes at floor lines) — a channel-shaped bond-beam block filled with grout and rebar that ties the wall together and carries loads to the piers. It is a separate line from field block and full-height core fill; count it by the course from your drawings.
Are cinder blocks and concrete blocks the same for estimating?
Yes. "Cinder block" is the surviving name for the lighter aggregate blocks of decades past; what you buy today is a concrete masonry unit (CMU) either way, in the same nominal 8 × 8 × 16 size — the counts from this cinder block calculator math are identical.
How tall can a concrete block wall be?
Unreinforced garden walls are commonly capped around 3–4 ft; taller or load-bearing walls need engineered reinforcement — vertical rebar in grouted cells, bond beams, and a footing sized to the load. Height, wind and retained earth all push the design past rule-of-thumb, so a freestanding wall over about 4 ft or any retaining wall wants an engineer.
How much does a concrete block wall cost?
Blocks run about $2–4 each in 2026 and mortar $6–9 a bag, so the default 20 × 8 ft wall is roughly $473 in block and $109 in mortar — before footing, core fill, rebar and labor. Laid by a mason, block walls typically price at $15–35 per square foot installed.
Sources and standards
The coverage figures and wall rules here come from the masonry industry’s published standards:
- ASTM C90: the standard specification for load-bearing concrete masonry units — the nominal 8 × 8 × 16 dimensions.
- TMS 402/602: the masonry code behind reinforcement, grouting and bond-beam practice.
- Quikrete published coverage: ~13 standard blocks per 80 lb bag of mortar mix, the mortar figure this calculator uses.
- Common estimating practice: 1.125 blocks per ft² of wall, 5% waste, and ~0.84 yd³ of grout per 100 blocks to fill all cores.
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