Concrete Wall Calculator

How it works

A poured wall is a slab standing on edge: its volume is thickness × height × length. Thickness is entered in inches and converted to feet, so the result is in cubic feet.

Windows and doors that are blocked out of the pour go right through the wall, so each removes its width × height × the wall thickness. The calculator adds up the face area of all openings, subtracts it from the wall's face area and multiplies the net area by the thickness.

The net volume is converted to cubic yards (27 cu ft per yard) and the waste allowance is added for the amount to order. Truck loads divide that by the truck capacity you enter and round up; the bag count divides the volume with waste by the yield of one bag and rounds up.

Formula

openings (sq ft) = Σ count × width × height
net (cu ft)      = (height × length − openings) × (thickness ÷ 12)
net (cu yd)      = net cu ft ÷ 27
to order         = net cu yd × (1 + waste ÷ 100)
truck loads      = ⌈ to order ÷ truck capacity ⌉
bags             = ⌈ net cu ft × (1 + waste ÷ 100) ÷ yield per bag ⌉
yield per bag: 40 lb ≈ 0.30, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft (QUIKRETE No. 1101, rev. Oct 2022)

Example

An 8 in wall 8 ft high and 40 ft long is (8 ÷ 12) × 8 × 40 = 213.33 cu ft before openings. Two 3 ft × 2 ft windows remove 12 sq ft × (8 ÷ 12) = 8 cu ft, leaving 205.33 cu ft, or 7.60 cu yd.

With 10% waste the amount to order is 8.37 cu yd, which is one load on a 10 cu yd truck. In 80 lb bags it would be 205.33 × 1.1 ÷ 0.60 = 376.4, so 377 bags.

Assumptions and limitations

• The wall is a single rectangle of constant thickness. Pilasters, brick ledges, thickened sections, the footing below and any wall that steps in height need to be calculated separately and added.
• A wall that tapers in thickness is entered at its average thickness, as the US Army's FM 5-428 Concrete and Masonry (1998) does in its retaining-wall example; for a straight taper this gives the exact volume.
• Each opening is a rectangular block-out through the full wall thickness, no wider than the wall and no taller than it. Bucks, lintels and partial-depth recesses are not modelled.
• Ready-mix truck capacity is entered by you; 8–10 cu yd is a typical range for a full-size mixer, and suppliers have minimum and partial-load charges that this count does not include.
• Bag yields are the approximate figures on the QUIKRETE Concrete Mix No. 1101 data sheet (revised October 2022): 0.30 cu ft per 40 lb bag, 0.45 per 60 lb and 0.60 per 80 lb. Other brands and mixes yield differently and the bag label governs.
• The waste allowance is a typical figure and is editable.
• This is a material estimate, not engineering. Wall thickness, height and reinforcement for a foundation or retaining wall depend on soil pressure and loads and are set by the applicable building code, the building official or a licensed engineer; the result is not a code determination.

Frequently asked questions