Concrete Calculator

How to estimate a concrete job with this calculator

A concrete estimate is area, cubic yards, the concrete itself, then base, reinforcement, forms, labor hours by task, overhead and margin. Most concrete calculators stop at the yards and the bags. This one keeps going to a price you can send, and it shows every step so you can argue with it.

1. Measure the slab. Length, width and thickness, or a diameter for a round pad. Tap a preset for a shed pad, patio, garage or driveway. The tool gives you square feet, feet of edge and net yards before you go further.
2. Pick the supply. Ready-mix truck or bags. Under 5 yards the plant adds a short-load fee; over 150 bags the tool tells you to call the plant.
3. Set the job. Gravel base, wire mesh or #4 rebar, forms, vapor barrier, expansion joint against an existing slab, the finish, whether the truck can reach, and how many people are on the crew.
4. Check your numbers. Open "Your numbers" and replace the ready-mix price, bag prices, material prices, production rates, loaded labor cost, overhead and margin with your own. Every default is labeled.
5. Read the price. The headline is what to send. Below it: yards or bags to order, person-hours, a customer-facing line item list, and a "your side" panel with cost, overhead, profit and the clock hours for your crew.
6. Copy the lines. Paste them into your estimate, or turn them into a WinPal estimate with your logo and terms.

Cubic yards = length × width × (thickness in inches ÷ 12) ÷ 27. Add 5 to 10% waste and round up to the quarter yard.

Price = (labor + materials + equipment + overhead) ÷ (1 − target margin). Divide, don't multiply. At 30% margin on $2,155 of cost, dividing by 0.70 gives $3,080. Multiplying by 1.30 gives $2,802, which is a 23% margin wearing a 30% name tag.

How much does it cost to pour a 20x20 concrete slab?

With the calculator's defaults, a 20x20 patio at 4 in with a compacted gravel base, wire mesh, new forms and a broom finish prices at $3,080 at a 30% margin, or $7.70 per sq ft. That's 5.5 yd of ready-mix and 16 person-hours, about five and a half clock hours for a crew of 3. Hypothetical job, real math.

Swap the mesh for a #4 rebar grid at 18 in and the same slab goes to $3,910 (660 lnft of bar, 18 person-hours). Make it a smooth trowel finish and it's $3,130. Put the truck on the street with a wheelbarrow run and it's $3,285. Each shows up as its own change in the customer lines, which is why the estimate lists them separately.

Concrete calculator: yards or bags?

Bags make sense up to roughly a yard, which is 45 bags of 80 lb. Past that you're mixing all day and the truck is cheaper per yard anyway. The calculator gives you both numbers so you can see the crossover on your own job.

The 80 lb yield is a standard-mix reference; the smaller sizes are proportional estimates. Confirm the actual yield on your bag, since products vary. The bag count includes waste and rounds up, so a 12x16 shed pad at 4 in is 118 bags of 80 lb, or 2.75 yd from the truck.

The short-load fee is the catch on the truck side. Plants set a minimum, often 4 to 6 yards, and charge a flat fee or a per-yard fee below it. The calculator adds $100 under 5 yd by default, so that 12x16 pad prices its concrete at 2.75 × $150 + $100 = $513. Order 5.5 yd for a 20x20 and the fee disappears. If a job sits just under the line, ask what a 5 yd order costs; sometimes the extra half yard is cheaper than the fee.

Waste is the other number people skip. Subgrade is never dead flat, chutes hold concrete, and a truck that comes up short at the far corner costs more than the 10% you should have ordered. The tool defaults to 10% and rounds up to the quarter yard.

Concrete slab cost calculator by size

At the calculator's defaults (4 in, gravel base, wire mesh, broom finish, truck access, crew of 3), the price per square foot falls as the slab grows, because forms, cleanup, equipment and the truck are mostly fixed. Every number below comes from the engine; the driveway row is a 10x40 at 4 in.

Two things to notice. The garage costs more per foot than the patio because 6 in of concrete is half again as much per square foot, and cars want it. And the 40x60 is a floor, not a quote: at 2,400 sq ft you're into a pump, four trucks timed back to back and more hands on the screed, and the calculator warns you about it.

A concrete driveway cost calculator is the same math with a preset: the 10x40 driveway above lands at $3,170. Thicken it to 5 in for a truck, or 6 in for anything heavier.

How the calculator works out concrete labor

Labor is priced by production rate per task, in person-hours, then divided by the crew to get clock time. That way a crew of 3 and a crew of 5 pay the same labor for the same slab; only the day gets shorter. All of the rates below are our starting points, labeled as assumptions in the panel. Time your crew on the next pour and replace them.

The total is rounded up to the half hour and priced at $32 an hour loaded, a mid-20s wage plus 25 to 30% for tax and insurance. That's what the hour costs you, not what you charge. For the 20x20 patio, 16 person-hours is 5.3 clock hours for a crew of 3: that is an allocation of working time, not a promise of elapsed job time. Curing, weather, return trips and form-removal timing need a separate schedule.

Finish type moves the finishing line only. Smooth trowel adds 25% to the finishing time, exposed or stamped adds 60%, and the tool flags stamped work because the stamps, color, release and sealer are not in that number. Wheelbarrow access doubles the placing time and nothing else, which is why a bad driveway costs the 20x20 about $200 more.

Common questions about concrete costs