Result
Result reflects the current submitted inputs.
- Risk B
- Reviewed 2026-05-26
- 1 sources
Breakdown
- Area
- 120 sq ft
- Volume before waste
- 40 cu ft
- Waste factor
- 10%
- The pour is rectangular with uniform thickness.
- Length and width are entered in feet; thickness is entered in inches.
- Quantity represents identical rectangular pours.
- Blank quantity is treated as 1 and blank waste factor is treated as 0%.
- Waste factor is a user-controlled estimating buffer, not an engineering rule.
- Results are material estimates only and are not engineering, code, or supplier ordering advice.
- Intermediate values are not rounded.
Accuracy notes
- Risk level
- B
- Reviewed
- 2026-05-26
- Sources
- 1
- Primary result
- Estimated order volume
Formula logic is kept in a pure calculator module with fixtures, source notes, and page-visible assumptions.
What the result means
The cubic yards or meters figure is what you'd order from a ready-mix truck (usually with a 1 yd^3 minimum). The bag count works for small DIY pours. Add waste; ready-mix is hard to top up once the truck leaves.
Use the result this way
- Start with Estimated order volume, then use supporting outputs for context.
- Verify Length, Width, and Thickness before copying the result.
- Check the formula, example, and assumptions before reusing the answer.
User job
How to use this calculator
Use Concrete Calculator when you need estimated order volume, then use concrete volume before waste and cubic yards before waste to check the context for unit checks, engineering notes, recipes, travel, shopping, and measurement cleanup.
Best for
- Converting compatible units
- Auditing the factor used for a repeated conversion
- Reviewing a default example before entering your own length and width.
Check before relying
- Make sure the source and target units measure the same kind of quantity.
- The pour is rectangular with uniform thickness.
- Length and width are entered in feet; thickness is entered in inches.
- Source context: Portland Cement Association, reviewed 2026-06-18.
Next useful step
- Square Footage CalculatorUse next when your task shifts from Concrete Calculator to Square Footage Calculator.
- Volume CalculatorUse next when your task shifts from Concrete Calculator to Volume Calculator.
- Area CalculatorUse next when your task shifts from Concrete Calculator to Area Calculator.
Formula
Slab volume: length x width x thickness. Convert to cubic yards by dividing by 27 (since 1 yd^3 = 27 ft^3) when working in feet. Round up and add a waste allowance of 5-10%. For 60 lb bags, each yields about 0.45 ft^3; an 80 lb bag yields about 0.6 ft^3.
- Slab: V = length x width x thickness (all same units). Convert to ft^3 first, then to yd^3 (divide by 27).
- Footing: treat as a long rectangular prism using length x width x depth.
- Column (round): V = pi x r^2 x h. Square column: side x side x height.
- Bag yields (approximate): 40 lb = 0.30 ft^3, 60 lb = 0.45 ft^3, 80 lb = 0.60 ft^3. Read the bag for the exact figure.
- Always add 5-10% waste; ready-mix trucks have a 1 yd^3 minimum. For pours over 1 yd^3 use ready-mix; smaller jobs use bags.
Inputs
Choose the shape (slab, footing, column, stairs), then enter dimensions. The calculator returns cubic volume, equivalent cubic yards/meters, and bag counts. Always pad your order by 5-10% to cover spill, uneven subgrade, and small estimation errors.
Example
A 10 ft x 12 ft x 4 inch slab is 10 x 12 x (4/12) = 40 ft^3, or 40/27 = 1.48 cubic yards. Add 10% waste: 1.63 yd^3. In 80 lb bags (0.6 ft^3 each), that's 40 / 0.6 = about 67 bags before waste, or about 73 with waste.
FAQ
How much concrete do I need?
Multiply length x width x thickness in feet to get cubic feet, then divide by 27 to get cubic yards. Add 5-10% for waste. A 10x12 ft slab 4 inches thick needs about 1.6 yd^3 with waste.
How many bags of concrete in a yard?
1 cubic yard is 27 cubic feet. An 80 lb bag yields about 0.6 ft^3, so 27/0.6 = about 45 bags. A 60 lb bag yields about 0.45 ft^3, so about 60 bags per yard.
How thick should a concrete slab be?
Residential patio or sidewalk: 4 inches. Driveways: 4-6 inches. Floors with heavy load (garage, shed): 5-6 inches. Always check local code and any structural requirements.
How much does a yard of concrete cost?
Prices vary by region, but ready-mix typically runs about $120-180 per cubic yard delivered, plus short-load fees for orders under a full truck. Bagged concrete is more expensive per yard but works for small jobs.
Should I add waste to my concrete order?
Yes. Add 5% for clean conditions, up to 10% for uneven subgrade or complex pours. Ready-mix is hard to top up once the truck leaves; running short means a costly second delivery.
What should I verify before using concrete calculator?
Verify length, width, and thickness, the displayed formula, and the worked example before copying the result into another document or decision.
Sources
Last reviewed: 2026-05-26
- officialReviewed 2026-06-18Concrete BasicsPortland Cement Association. Concrete proportions and slab thickness guidance.
Disclaimer
Estimates are based on the dimensions you enter and approximate bag yields. Actual concrete needed depends on subgrade, screed thickness, and form accuracy. Always confirm with your supplier and add a waste allowance.