Concrete Calculator

A cubic yard is 27 cubic feet and an 80 lb bag yields about 0.60 cubic feet, so a cubic yard takes roughly 45 bags of 80 lb concrete. In 60 lb bags it is about 60 bags, and in 40 lb bags about 90. At that point ready-mix is almost always cheaper and far less work.

Multiply length × width × thickness with every measurement in the same unit, then divide by 27 for cubic yards. The usual mistake is leaving thickness in inches — divide inches by 12 first. A 10 × 10 ft slab at 4 in is 10 × 10 × 0.333 = 33.3 cubic feet, or 1.23 cubic yards.

Patios, walkways and shed floors are usually 4 inches. Driveways and any slab that carries vehicles are typically 5–6 inches over a compacted gravel base. Structural slabs and footings are set by local code — check before you pour.

Yes. Use the imperial/metric switch above the form and the whole page changes: inputs take metres and centimetres, and results come back in cubic metres and tonnes. Bag sizes stay in pounds because that is how pre-mix concrete is sold in North America.

A round form holds π × radius² × height. A 12 in tube holds about 0.79 cubic feet per foot of depth, a 10 in tube about 0.55, and an 8 in tube about 0.35. Choose "Round column, pier or tube" above and enter the diameter, height and how many you are pouring.

Yes — a 5–10% waste allowance covers spillage, an uneven subgrade and over-excavation. Running short mid-pour leaves a cold joint, which is far worse than having a little left over. This calculator adds your chosen waste percentage automatically.

Bags usually win below about a cubic yard, which is roughly 45 bags of 80 lb. Above that, ready-mix is normally cheaper and much faster once the short-load fee is spread across the load. Suppliers commonly add that fee under 4–5 cubic yards.

No — a cubic metre is about 31% bigger. One cubic yard is 0.765 cubic metres, and one cubic metre is 1.308 cubic yards. Mixing the two up is one of the most expensive ordering mistakes there is, which is why this calculator converts both ways for you.