Cinder Block Wall Calculator

About the Cinder Block Wall Calculator

Cinder blocks are a fast, low-cost way to build garden walls, sheds, garages and foundations. Before the first block is laid, though, you need to know three things: how many blocks to buy, how much they will weigh, and what they will cost. Weight matters more than people expect. A small wall can easily add up to more than a ton of blocks, which decides how they are delivered and whether a pickup or trailer can carry them safely.

This cinder block wall calculator counts the blocks for a wall from its length and height, leaving out doors and windows and adding a waste allowance. It then gives the total weight for lightweight cinder or dense concrete blocks, the number of pallets and the cost of the blocks.

How to Use the Cinder Block Wall Calculator

Enter the wall length and wall height in feet.

Enter the area of any doors and windows to leave out, in square feet.

Choose the block type, and enter the waste allowance and the price per block.

The Formulas

  wall area   = length × height − openings
  blocks      = ⌈wall area × 1.125 × (1 + waste)⌉
  weight      = blocks × block weight
  pallets     = ⌈blocks ÷ 90⌉
  cost        = blocks × price

A standard block with its mortar joint covers 8 × 16 inches, which is 0.889 square feet, so 1.125 blocks cover each square foot.

Step-by-Step Example

A 20 × 4 ft wall in lightweight cinder blocks, 5% waste, $2.50 a block.

  area     20 × 4 = 80 ft²
  blocks   80 × 1.125 × 1.05 = 94.5 → 95
  weight   95 × 28 = 2,660 lb (1.33 tons)
  pallets  95 ÷ 90 → 2
  cost     95 × $2.50 = $237.50

Cinder Blocks Versus Concrete Blocks

Originally, cinder blocks were made with coal cinders, the ash left from furnaces and power plants, as the aggregate. They were lighter than solid concrete but weaker. Today true cinder blocks are rare, and the name is used loosely for any hollow concrete masonry unit. Blocks made with lightweight aggregates such as expanded shale, clay or slag weigh about 25 to 30 pounds for a standard 8 × 8 × 16 inch unit. Normal-weight blocks made with sand and gravel weigh about 35 to 40 pounds. Both are often sold side by side, so check the label or ask the supplier.

Why Weight Matters

The weight of the blocks affects every stage of the job. A pallet of 90 lightweight blocks weighs around 2,500 pounds; a pallet of dense blocks over 3,400 pounds. That is more than most pickups can safely carry, so pallets are usually delivered by a truck with a forklift or crane. On site, the weight of the finished wall bears on the footing, and a heavier wall needs a footing sized for it. Lighter blocks are also easier on the back over a long day of laying.

Openings and Waste

Doors, windows and vents reduce the number of blocks, so the calculator subtracts their area. Openings need lintels, special bond-beam blocks or precast concrete beams over the top, which are bought separately. The waste allowance covers blocks broken in delivery and handling, and cuts at ends and openings. Five percent is usual for a simple wall; walls with many corners and openings may need 10%.

Pricing

Block prices vary with type, size, region and quantity. Lightweight blocks often cost a little more than dense blocks, and decorative split-face or coloured blocks cost several times more. Buying full pallets usually earns a lower price per block. Remember to budget for mortar, sand, rebar, grout, caps and the footing, which together can cost as much as the blocks themselves.

Delivery and Storage

Plan where the pallets will be set down, on firm, level ground close to the wall, and keep blocks covered and off wet ground until use. Blocks that are soaked before laying can cause mortar problems and efflorescence, the white bloom that appears as water dries out of masonry.

Insulation and Finishing

Hollow blocks are poor insulators on their own. For a garage or workshop that will be heated, the cores can be filled with loose insulation or foam inserts, or rigid foam board can be fixed to the inside face. Outside, blocks can be left plain, painted with masonry paint, or covered with stucco for a smoother finish. Painting or rendering also helps keep rain out of the porous blocks.

Building Codes

A garden wall a few courses high rarely needs a permit, but sheds, garages, retaining walls and anything over local height limits usually do. The building department may specify the block type, footing size, reinforcement and grouting, so check before you order blocks. The concrete block wall calculator estimates the grout and rebar for a reinforced wall.

Understanding Your Result

The headline gives the number of blocks.

The count line shows the area, blocks per square foot and waste.

The weight line gives the total weight and pallets.

The cost line gives the cost of the blocks.

When Should You Use This Calculator?

Use it when ordering blocks for a wall, shed or garage.

Use it to check whether a vehicle or trailer can carry the load.

Use it to compare the weight and cost of lightweight and dense blocks.

Common Mistakes

Assuming all grey blocks weigh the same. Lightweight and dense blocks differ by 10 pounds.

Forgetting openings. Subtract doors and windows.

Overloading a pickup. A pallet can weigh over a ton.

Budgeting only for blocks. Mortar, grout and footings add up.