Concrete Slab Cost Calculator

This concrete slab cost calculator works out the concrete your slab needs, then prices it two ways: in bags and by ready-mix truck, including the short-load fee suppliers add to small orders. It adds a gravel base, rebar or mesh, labor and extras, and shows the slab size at which the truck becomes the cheaper choice at your prices.

About the concrete slab cost calculator

Most concrete slab cost calculators multiply a volume by one price. The real question on a patio or a shed base is usually different: do you mix bags yourself or call a truck? For a small slab that depends on one fee most calculators leave out.

• Bags against the truck, priced side by side, with the cheaper one in the total.
• The short-load fee, charged when your order is under the supplier’s minimum.
• The crossover point: the slab size where the truck starts to win, at your prices.
• Real ordering rules: bags in whole numbers, ready-mix in the supplier’s steps, usually a quarter yard.
• Gravel base, rebar grid or wire mesh, labor and extras.
• Rectangle or round slabs.

The prices filled in are examples, so the page shows a result. Put in your own quotes. It runs in your browser and nothing is saved.

How to use the concrete slab cost calculator

1. Enter the slab: length and width in feet, or a diameter, and the thickness in inches.
2. Put in your prices: a bag of concrete, ready-mix per cubic yard, your supplier’s minimum order, short-load fee and delivery fee.
3. Open the extras for gravel, rebar or mesh, labor and anything else.
4. Read the total and the cost a square foot, and see which way of buying concrete is cheaper.

A worked example

A 10 x 10 ft patio, 4 in thick, with 10% extra for waste, a 4 in gravel base and a rebar grid at 18 in. These are the page’s defaults, and the prices are examples.

1. Volume: 10 × 10 × 4 ÷ 12 ÷ 27 = 1.23 cubic yards. With 10% extra, 1.36 cubic yards, or 36.7 cubic feet.
2. Bags: an 80 lb bag yields about 0.60 cubic feet, so 36.7 ÷ 0.60 = 61.1, which rounds up to 62 bags. At $6.50 a bag, $403.
3. Truck: the order rounds up to 1.5 yards. At $165 a yard that’s $247.50, plus a $150 short-load fee for ordering under 4 yards: $397.50.
4. Rebar: 7 bars each way at 18 in, 146 feet with laps, so 8 bars of 20 ft: $96.
5. Gravel base: 1.23 cubic yards at $50: $61.73.
6. Total: $555.23, or $5.55 a square foot, using the truck.

With these prices the truck wins narrowly, even with the fee. Lower the bag price or raise the fee and bags take over. The crossover here is 1.25 cubic yards, about 92 square feet at 4 in.

Bags or ready-mix: where the line falls

Two things move the line:

• The short-load fee. Below the supplier’s minimum, every small order carries it. On a tiny slab it can be most of the bill.
• The labor of mixing. 62 bags of 80 lb is about 2.5 tons to lift, mix and place, and it all has to go in before the first batches set. A truck pours in minutes.

A bigger slab with the same example prices, 20 × 24 ft at 4 in, needs 6.52 cubic yards. That’s 294 bags ($1,911) against 6.75 yards by truck ($1,113.75) with no short-load fee. Bags make little sense at that size.

What a short-load fee is

A ready-mix truck costs a supplier about the same to send whether it carries 2 yards or 9. So suppliers set a minimum order and charge a short-load fee below it. Each supplier sets both figures, and they vary. Ask for the minimum, the fee, any delivery or fuel charge, and how long the driver waits before charging for time. Put the figures into the concrete slab cost calculator and it tells you whether ordering up to the minimum is cheaper than paying the fee.

How thick should the slab be?

Those are the volumes before waste. Check the thickness your project and local code call for. This calculator prices a slab; it doesn’t design one for loads or soil.

Rebar or wire mesh

• Rebar grid: bars both ways at a set spacing, held off the ground on chairs so they sit in the middle of the slab. The calculator allows 3 in of cover at the edges and 10% extra for laps, in 20 ft bars.
• Wire mesh: sheets of 5 × 10 ft, lapped 6 in each way, so each covers about 42.75 square feet.

The gravel base

A layer of compacted gravel under the slab drains water and gives an even, firm surface. Four inches is common. The calculator gives its volume in cubic yards. For tons and coverage, our rock calculator and the guide on how much rock you need cover gravel weights.

What else adds to the cost

• Excavation and grading if the ground isn’t level.
• Forms: lumber and stakes around the edge.
• A pump if the truck can’t reach the pour.
• Finishes: broom, stamped or colored concrete cost more.
• A permit where your area requires one.
• Sealer and control joints.

Put any of these in “Other costs” and they join the total.

Common mistakes

• Forgetting the short-load fee. On a small order it can double the concrete bill.
• Ordering exactly the volume. Ground is never perfectly flat. Add 5 to 10%.
• Running out of bags mid-pour. Round up and buy one or two extra.
• Using nominal thickness for a sloped site. Measure the depth at several points.
• Comparing quotes per square foot without the thickness. A 6 in slab uses 50% more concrete than a 4 in one.

How the concrete slab cost calculator works

1. Volume: area × thickness ÷ 12 ÷ 27, plus waste.
2. Bags: cubic feet ÷ the bag’s yield, rounded up. Quikrete’s data sheet gives 0.30 cubic feet for 40 lb, 0.375 for 50 lb and 0.45 for 60 lb, which is 0.0075 per pound, so 80 lb is 0.60 and 90 lb is 0.675.
3. Ready-mix: the order rounds up to your step, plus the short-load fee if under the minimum, plus delivery.
4. Crossover: the smallest volume, in 0.05 yard steps, where the truck costs no more than bags.
5. Total: the cheaper concrete, plus steel, base, labor and extras.

Just need the volume? The cubic yard calculator handles several areas at once, and the volume of a cylinder calculator does round footings and tube forms.