Everyday
Concrete Block Calculator
Enter your wall's length and height, and the page works out how many blocks to order, how many pallets that means for delivery, the mortar and grout bags, the rebar for the grouted cores, and the cap blocks for the top course.
How it works
Behind the numbers
Block count comes from the nominal face. A standard 8x8x16 block covers 8 by 16 inches of wall, and that nominal size already includes the 3/8-inch mortar joint, so 1.125 blocks cover each square foot and 112.5 cover 100 square feet. Every width from 4 to 12 inches uses the same 8x16 face, so the count is identical across block sizes. Waste defaults to 5%; walls with many openings or corners deserve 10%. The waste allowance applies to the block count only; mortar, grout and rebar are computed from the raw count.
Mortar is estimated at 0.028 eighty-pound bags per block, which matches contractor rules of thumb of about 3 bags per 100 blocks at 3/8-inch joints and includes normal waste. Grout assumes 0.4 eighty-pound bags per 8-inch block at full core fill, scaled by wall width and the fill percentage you choose; solid blocks skip grout entirely. Vertical rebar is placed at the spacing you choose (commonly every 48 inches in grouted cores), each bar runs the wall height plus 1.5 feet of lap, and a bond beam course is figured every 4 feet of wall height. Sticks are 20-foot lengths, rounded up.
Pallets use typical industry cubes: 90 for 8-inch block, 114 for 6-inch, 132 for 4-inch and 54 for 12-inch, though cubes range widely by manufacturer, so confirm with your supplier. A hollow 8x8x16 block typically weighs 28 to 38 pounds, and a full pallet lands between 2,500 and 3,500 pounds, which is why delivery usually means a flatbed and a forklift. A flatbed carries roughly 20 cubes. Cap blocks are 16 inches long, so 0.75 of a block covers each linear foot of wall top. These are planning numbers for ordering materials, not a structural design; tall or load-bearing walls need an engineer's specification and local code governs rebar placement.
FAQ
Questions, answered
How many concrete blocks do I need for a 10x10 wall?
A 10 by 10 wall is 100 square feet, which takes 112.5 blocks at the standard 8x8x16 size. With the default 5% waste allowance, order 119. Walls with doors, windows or many corners should use 10% instead, which comes to 124.
How many 8x8x16 blocks come on a pallet?
The industry standard cube holds 90, though manufacturers ship anywhere from 72 to 108. Hollow 8x8x16 blocks weigh 28 to 38 pounds each, so a full pallet weighs roughly 2,500 to 3,500 pounds plus the pallet. That is why you need a forklift or pallet jack on site, and why a pickup truck cannot carry a full pallet.
How much mortar do I need per concrete block?
At 3/8-inch joints, figure about 3 eighty-pound bags per 100 blocks, or one bag per 35 blocks. This calculator uses 0.028 bags per block, which includes normal waste from spillage and repointing. Order a bag or two extra if the crew is inexperienced.
Do concrete block walls need rebar?
Structural and retaining walls do: vertical bars are commonly placed every 48 inches in grouted cores, with a horizontal bond beam every 4 feet of wall height. Short freestanding garden walls may not need steel. Local code decides; the defaults here are a planning starting point, not an engineered specification.
How many bags of grout fill one block's cores?
A standard 8x8x16 block holds about 0.27 cubic feet of core volume, and an 80-pound bag of grout yields about 0.6 cubic feet, so roughly 0.4 bags fill one block's cores completely. Bagged grout makers rate one 80-pound bag at about 3 blocks, so the real-world range is 0.33 to 0.5 bags per block. This calculator uses 0.4 and rounds up.