How Much Concrete Do I Need?
Measure each part of the project, enter the shape and dimensions, then let the calculator add the sections together. The result shows net concrete volume, volume with your waste allowance, an estimated ready-mix order amount, and the number of premixed bags based on the finished yield you enter.
Use separate sections when a project has different shapes or repeated parts, such as a slab plus post holes. The calculator totals exact section volumes before rounding bags, so small sections are not rounded one by one.
How to Calculate Cubic Yards of Concrete
For a rectangular slab, wall, or footing, convert all dimensions to feet first:
length ft x width ft x thickness ft = cubic feet
Then convert cubic feet to cubic yards:
cubic feet / 27 = cubic yards
Round columns and round footings use the cylinder formula. Post holes can subtract the embedded volume of a round or square post when you enter those dimensions.
Concrete Bags: Sizes and Yield
Bag counts should be based on finished concrete yield, not just bag weight. QUIKRETE lists approximate yields of 0.30 ft3 for 40 lb, 0.375 ft3 for 50 lb, 0.45 ft3 for 60 lb, and 0.60 ft3 for 80 lb Concrete Mix bags in its product data sheet. Sakrete High-Strength Concrete Mix lists 0.30 ft3 for 40 lb, 0.45 ft3 for 60 lb, and 0.6 ft3for 80 lb bags.
Always check the yield printed on the product you plan to buy. This calculator lets you edit yield because bag sizes, product lines, and regional products can vary. Bags are rounded up after the project volume and waste allowance are summed.
Sources: QUIKRETE Concrete Mix No. 1101 data sheet and Sakrete High-Strength Concrete Mix technical data sheet.
Bagged Concrete vs. Ready-Mix
Bagged concrete is practical when you want to mix smaller amounts on site or handle separate small sections. Ready-mix is ordered by volume, usually in cubic yards, and can make more sense when the total volume is large enough for delivery and placement logistics.
The calculator shows both views so you can compare the material quantity. It does not estimate local delivery minimums, short-load fees, labor, pump requirements, or local prices.
How Much Extra Concrete Should I Allow?
The waste allowance covers measurement variation, uneven excavation, form movement, spillage, and small placement losses. Enter the percentage you want to carry, and the calculator applies it once to the total project volume.
Because extra concrete is project-specific, this tool does not prescribe a structural design allowance. Confirm final order quantities, supplier increments, and site conditions before buying material.
Concrete and Cement: What's the Difference?
Cement is one ingredient in concrete. Concrete is the finished construction material made from cement, aggregates, water, and any product-specific additives. This page estimates concrete volume and premixed concrete bags, not separate cement, sand, and aggregate proportions.
Calculated Example
10 ft x 10 ft slab at 4 inches thick
- Convert 4 inches to feet: 4 / 12 = 1/3 ft, approximately 0.333 ft.
- Find net volume: 10 x 10 x 1/3 = 33.33 ft3. The calculation keeps full precision until the result is displayed.
- Convert to cubic yards: 33.33 / 27 = 1.23 yd3 net.
- Add 10% waste: 33.33 x 1.10 = 36.67 ft3, or 1.36 yd3 rounded up for ready-mix display.
- For 80 lb bags at 0.60 ft3 each: 36.67 / 0.60 is approximately 61.11, rounded up to 62 bags.
FAQs
How many 80 lb bags are in one cubic yard?
Without waste, one cubic yard takes 45 bags when each 80 lb bag yields 0.60 ft3, because 27 / 0.60 = 45. With the calculator's default 10% waste, the same cubic yard becomes 50 bags.
How much area does one cubic yard of concrete cover at 4 inches thick?
It covers 81 ft2, assuming uniform thickness and no waste. Four inches is 1/3 ft, so 27 ft3 / (1/3 ft) = 81 ft2.