Concrete Driveway Calculator

How it works

The slab is a rectangle: length × width gives the area, and area × thickness (inches converted to feet) gives cubic feet, which is converted to cubic yards at 27 cu ft per yard. The thickness comes from the preset you pick or the custom value. The waste allowance is added for the concrete to order.

The gravel base is the same area at the base depth, converted to cubic yards and then to tons using the base density you enter. Wire mesh is laid in strips running the length of the slab, side by side across its width, each lapping the one before: the number of strips is the width less one lap divided by the mesh width less one lap, rounded up (one strip when the slab is no wider than the mesh). The strips are laid one after another. A strip starts with a fresh roll or sheet, or with the offcut left from the previous strip, which counts at its full length; every further piece laps the one before and adds its length less one lap. The piece that finishes a strip is cut there and its offcut starts the next strip, so that cut costs a lap that a continuous run would not. The count is never more than (strips × length − one lap) divided by (piece length − one lap), rounded up. A rebar grid places one bar more than the number of spaces in each direction, adds up their lengths and divides by the stock bar length, rounded up.

Control joints divide the slab into panels no longer than the joint spacing in either direction. The number of joints across each dimension is the number of panels less one; the joint length adds the width for each transverse joint and the length for each longitudinal one. The material cost multiplies each quantity by the price you enter.

Formula

concrete (cu yd)  = length × width × (thickness ÷ 12) ÷ 27
to order          = concrete × (1 + waste ÷ 100)
base (tons)       = length × width × (base depth ÷ 12) ÷ 27 × density
mesh strips       = 1 if W ≤ mesh width, else ⌈(W − lap) ÷ (mesh width − lap)⌉
mesh pieces       = laid strip by strip: first piece (or carried offcut) adds its full length,
                    each further piece adds (mesh length − lap); the finishing cut's offcut starts the next strip
                    ≤ max(1, ⌈(strips × L − lap) ÷ (mesh length − lap)⌉)
rebar (ft)        = (⌈W ÷ s⌉ + 1) × L + (⌈L ÷ s⌉ + 1) × W;  bars = ⌈ rebar ÷ bar length ⌉
joints            = (⌈L ÷ j⌉ − 1) + (⌈W ÷ j⌉ − 1);  joint length = (⌈L ÷ j⌉ − 1) × W + (⌈W ÷ j⌉ − 1) × L
cost              = to order × $/cu yd + tons × $/ton + pieces × $ each

Example

A 40 ft × 12 ft driveway at 4 in is 480 sq ft and 160 cu ft, or 5.93 cu yd; with 10% waste, 6.52 cu yd to order. A 4 in gravel base is another 5.93 cu yd, which at 1.5 tons per cu yd is 8.89 tons.

With 5 ft mesh lapped 6 in, the 12 ft width takes ⌈11.5 ÷ 4.5⌉ = 3 strips, each 40 ft long. One 150 ft roll lays the first strip and its 110 ft and then 70 ft offcuts lay the other two, so one roll. In 5 ft × 10 ft sheets the first strip takes a whole sheet and four lapped ones (10 + 4 × 9.5 = 48 ft, leaving an 8 ft offcut), the second the offcut and four more (6 ft left), the third the offcut and four more: 13 sheets. Joints at 10 ft make four panels along the length and two across, so three transverse joints of 12 ft and one longitudinal joint of 40 ft: 4 joints, 76 ft.

At the illustrative prices of $150 per cu yd, $30 per ton and $100 per roll the materials come to 6.52 × 150 + 8.89 × 30 + 100 = $1,344.44.

Assumptions and limitations

• The slab is a rectangle of uniform thickness on a base of uniform depth. Thickened edges, curves, flares at the street and sloped sub-grades are not modelled.
• Thickness presets are typical figures — about 4 in for passenger vehicles and 5–6 in where trucks park — not a design. The right thickness depends on the loads, the sub-grade and local requirements.
• Base tons use the density you enter for the compacted base. The default of 1.5 tons per cu yd is a typical figure; suppliers can give the figure for their material.
• Mesh is laid in full-width strips along the slab with the lap at every side and end joint. The piece that finishes a strip is cut there and its offcut starts the next strip; that cut costs a lap that one continuous run would not. No piece is cut lengthwise to make a narrower strip, so the last strip may overhang the slab edge. Edge cover and chairs are not counted.
• Rebar length ignores edge cover, lap splices and chairs. The bar count is the total length divided by the stock length: offcuts are assumed spliced into other runs; cutting each run from stock without splices needs more bars, and splice laps add length.
• Joint spacing is a typical figure you can change. US Army FM 5-428, Concrete and Masonry (1998), Table 4-13 lists 10–15 ft for a 5 in slab and 12–18 ft for a 6 in slab depending on aggregate size and slump — about 2–3 ft per inch of thickness; the QUIKRETE Concrete Mix No. 1101 data sheet (rev. October 2022) says to cut control joints every 6–8 ft. Joint depth and layout around corners and fixtures are not modelled.
• Prices are illustrative defaults, not market data. Delivery, pump, short-load and labour charges, forms, sealant, vapour barrier and finishing are not included.
• This is a material estimate, not engineering. Slab thickness, base and reinforcement for vehicle loads may be governed by local codes or a licensed engineer's design; the result is not a code determination.

Frequently asked questions