Concrete Calculator

Multiply length by width by thickness, with every dimension in feet, then divide by 27 to get cubic yards (a cubic yard is 3 by 3 by 3 feet). A 4 inch slab uses 4 ÷ 12 = 0.33 feet for thickness, so a 20 by 10 foot slab holds 2.47 cubic yards. Add about 10 percent for waste and you order 2.75 cubic yards. Round columns use π × radius² × height; solid stairs use width × run × rise × N × (N + 1) ÷ 2.

It takes 45 eighty-pound bags, 60 sixty-pound bags, or 90 forty-pound bags to make one cubic yard. A cubic yard is 27 cubic feet, and each bag yields 0.60, 0.45, or 0.30 cubic feet, so 27 ÷ 0.60 = 45, 27 ÷ 0.45 = 60, and 27 ÷ 0.30 = 90. Always round bag counts up.

Bags make sense for small jobs like a few post footings or a landing. Once you pass roughly one cubic yard, ready-mix from a truck is usually cheaper and far less work than mixing dozens of bags by hand. Ready-mix suppliers also have a minimum load of about one cubic yard and add a short-load fee on small pours, so bags often win for a tiny job.

Order by the cubic yard and round up to the next quarter yard. A standard truck holds about 8 to 11 cubic yards, so give the supplier your total, the mix strength (PSI), and the pour date. Most set a minimum and add a short-load fee of $40 to $60 per cubic yard under a full truck. Order about 10 percent extra, since you cannot add concrete to a pour once it starts setting.

Order more than the plan dimensions call for. The NRMCA recommends 4 to 10 percent over, and this calculator defaults to 10 percent. Flatwork on prepared subgrade can use 5 percent, while footings and work placed against excavated soil run higher. Ready-mix is sold in quarter-yard steps, so round the order up to the next 0.25 cubic yard. You cannot add concrete to a pour once it starts setting.

Yes. Slabs, footings, and walls are all rectangular pours, so use the Slab, Wall & Footing mode and enter length, width, and thickness. The field order does not change the volume, and the math is identical.

Yes. Use Column mode for any round pour: a concrete column, pier, post footing, or a Sonotube or Quik-Tube form. Enter the tube diameter and height for a solid pour. Switch to Hollow and add the inner diameter to subtract an open core, which is what you need for a pipe, a sleeve, or a pier with a void.

Yes. Use Round Slab mode and enter the diameter in feet and the thickness in inches. The calculator uses π × radius² × thickness, which is what you need for a round patio, a pad, or a tank base.

Yes, for a solid poured stoop with steps down to grade. It computes the full solid mass under the stair profile: width × run × rise × N × (N + 1) ÷ 2, where N is the number of steps. If your stoop has a top landing deeper than one tread, add that platform separately in Slab, Wall & Footing mode. Open-stringer or suspended stairs use far less concrete.

Choose Thickened Edge and enter the slab length, width, and thickness, then the turndown edge width and the total edge depth. The calculator adds the flat slab plus the extra depth of the perimeter turndown that drops below it, so the slab is never double-counted. This is the monolithic footing poured under garage, shed, and home slabs on grade.

Normal-weight concrete weighs about 150 pounds per cubic foot, so a cubic yard weighs roughly 4,050 pounds, just over two tons. In metric that is about 2,400 kilograms per cubic metre. The calculator shows the net weight of your pour.

Enter your price per cubic yard for ready-mix, or your price per bag, in the optional price field, and the calculator multiplies it by the rounded order. As a 2026 benchmark, ready-mix runs about $160 to $195 per cubic yard in the US, though prices vary by region. Delivery, short-load fees, and pumping are billed separately by your supplier.

A common rule of thumb for hand-mixing from separate materials is 1 part cement, 2 parts sand, and 4 parts aggregate by volume, which makes a general-purpose mix. You do not need it to use this calculator: bagged concrete and ready-mix both arrive pre-proportioned, so the volume shown is the same whatever the mix strength.

Yes. Switch the toggle to metric and enter metres and millimetres. You get cubic metres to order, the 20, 25, or 30 kg bag count, and the weight in kilograms.

Yes. It is free, needs no signup, and runs entirely in your browser. Nothing you type is uploaded anywhere.

No. This calculator works from dimensions you type in. To pull slab, footing, and wall dimensions straight off a PDF plan to scale, use Easy Takeoffs, the construction takeoff software built to measure off plans. 14-day trial, no card.