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Concrete Calculator

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Enter the dimensions of a slab, footing, or column to find how much concrete you need - in cubic yards, cubic feet, and pre-mixed bags.

Concrete Calculator

Live
Cubic yards needed
1.48
Cubic feet
40.00
60 lb bags
89
Most suppliers recommend ordering 5-10% extra to cover spillage and uneven subgrade.

The formula

Cubic feet = Length x Width x Thickness (in feet) Cubic yards = Cubic feet / 27 60 lb bags = Cubic feet / 0.45
Example

A 10 ft x 12 ft slab at 4 inches thick: cubic feet = 10 x 12 x 0.333 = 40 cu ft. That's 1.48 cubic yards, or about 89 bags of 60 lb pre-mix.

Step-by-step guide

  1. Measure the length and width of the area to be poured.
  2. Measure the thickness - 4 inches is standard for patios and walkways, while driveways often use 5-6 inches for the extra vehicle load.
  3. Read the volume needed, then order 5-10% extra to cover waste and an uneven subgrade.

Ready-mix vs. bagged concrete

For anything larger than about 1 cubic yard, ready-mix delivered by truck is usually more cost-effective and far less physical labor than mixing dozens of bags by hand. Most ready-mix suppliers have a minimum order (often 1 yard) and may charge a short-load fee below that. For smaller jobs - a mailbox post footing, a small patch, a single step - bagged concrete mixed on-site makes more sense. This calculator gives you both figures so you can decide which fits your job.

Common mistakes

Forgetting to convert thickness from inches to feet before multiplying - mixing units is the most common source of a wildly wrong result.
Ordering the exact calculated amount with zero buffer - an uneven subgrade, form flex, and spillage routinely use 5-10% more than the math suggests.

Frequently asked questions

How thick should my concrete slab be?

4 inches is standard for patios, walkways, and shed floors. Driveways handling vehicle weight typically use 5-6 inches, and areas with heavy truck traffic may need more - check local building codes for your specific use.

How much does a bag of concrete actually cover?

A standard 60 lb bag yields about 0.45 cubic feet of mixed concrete, and an 80 lb bag yields about 0.6 cubic feet. This calculator uses the 60 lb figure; scale accordingly if you're using 80 lb bags.

Do I need rebar or wire mesh?

For most residential slabs 4 inches or thicker, reinforcement (rebar or welded wire mesh) is commonly recommended to control cracking, especially in areas with freeze-thaw cycles or unstable soil. Check local codes and consider consulting a professional for structural pours.

How long does concrete take to cure?

Concrete typically reaches enough strength to walk on within 24-48 hours, but continues curing for about 28 days to reach its full design strength. Avoid heavy loads (vehicles, furniture) before that point.

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