This is the main concrete calculator on Concrete Yard Planner. Use the estimator below for any flat pour, then keep reading for the volume formula, bag conversions, and planning checks you need before ordering ready-mix or buying bagged concrete. For project-specific tools, jump to the slab calculator, footing calculator, or bag calculator.
Estimate Your Concrete Now
Enter length, width, and depth (or thickness) for any rectangular pour to get cubic yards, cubic feet, and bag counts. Need a project-specific tool? Use the links below the estimator.
Quick Concrete Estimator
Estimates only. Bag yields vary by brand and mix. Always confirm with your supplier.
Different project type?
Slab Calculator
Footing Calculator
Bag Calculator
All Calculators
Quick Answer: Key Conversions
1 cubic yard = 27 cubic feet
- 80 lb bag: ~0.60 ft³ (about 45 bags per cubic yard)
- 60 lb bag: ~0.45 ft³ (about 60 bags per cubic yard)
- 40 lb bag: ~0.30 ft³ (about 90 bags per cubic yard)
Important: Always confirm the actual yield printed on your bag label, since concrete mixes vary by brand and product type.
The Concrete Volume Formula
Every concrete estimate comes down to one core formula. Once you know it, you can sanity-check any calculator result in seconds, regardless of project type.
Volume (ft³) = Length (ft) × Width (ft) × Depth (ft)
To convert to cubic yards (the unit ready-mix suppliers use), divide by 27:
Volume (yd³) = Volume (ft³) ÷ 27
Quick unit conversions to keep handy:
- Inches to feet: divide by 12 (a 4-inch slab is 0.333 ft thick)
- Yards to feet: multiply by 3
- Square feet to square yards: divide by 9
Finally, multiply your final volume by 1.05 to 1.10 to add a five to ten percent waste factor. This buffer covers spillage, uneven subgrade, and small measurement errors.
How to Estimate Concrete in 3 Steps
Measure Your Project
Measure length, width, and depth or thickness of the area you plan to pour. Keep all dimensions in the same unit before calculating, and measure inside any forms rather than outside.
Calculate Volume
Multiply length × width × depth in feet to get cubic feet, then divide by 27 for cubic yards. Use the calculator above to skip the math and avoid unit-conversion mistakes.
Add Waste and Round Up
Add a 5–10% buffer for spillage, uneven subgrade, and small measurement errors. Round up before ordering so you do not run short mid-pour and create a cold joint.
Bags vs Ready-Mix: When to Switch
Choosing between bagged concrete and ready-mix delivery is mostly a question of volume, labor, and access. Bagged concrete works for small repairs and isolated pours. Ready-mix becomes more practical as soon as the volume grows or the pour needs to stay continuous.
Use Bagged Concrete When:
- Project is under 1–2 cubic yards
- No truck access is available
- You want to work at your own pace
- Pour is small, segmented, or repair-focused
Switch to Ready-Mix When:
- Project exceeds 2 cubic yards
- A continuous pour is important
- Labor savings matter more than flexibility
- You need consistent batching and faster placement
Rule of thumb: Above 2 cubic yards, ready-mix usually wins on time, labor, and consistency. For pricing context, see our concrete cost per yard guide.
Worked Examples Across Project Types
Three quick scenarios using the same core formula, one for each main project type. Click through to the dedicated calculator when you are ready to enter your own numbers.
Patio Slab — 10 × 10 ft (4″ thick)
Volume: 10 × 10 × 0.333 = 33.3 ft³ → 1.23 yd³
+10% waste: ≈ 1.35 yd³ → order 1.5 yd³.
Bag Conversion — 0.50 yd³
80 lb bags: 0.50 × 45 ≈ 23 bags
60 lb bags: ≈ 30 · 40 lb bags: ≈ 45.
4 Deck Footings — 12″ × 12″ × 24″
Volume: (1 × 1 × 2) × 4 = 8 ft³ → 0.30 yd³
+10% waste: ≈ 0.33 yd³ → about 14 × 80 lb bags.
Frequently Asked Questions
How do you calculate concrete?
Multiply length, width, and depth in feet to get cubic feet, then divide by 27 to convert to cubic yards. Add a five to ten percent waste factor. For bagged concrete, divide your cubic feet result by the yield printed on the bag (typically 0.6 ft³ for an 80 lb bag).
How accurate are concrete calculators?
Concrete calculators use standard volume formulas and are reliable for planning and ordering when your measurements are correct. Final material needs can still vary because of waste, over-excavation, site conditions, and the actual yield of the product you buy.
Why do I need a waste factor?
Real projects rarely match perfect math. Minor spills, uneven forms, soft subgrade, and measurement differences can all increase the amount of concrete needed, so a 5–10% buffer is standard practice.
What is the difference between cubic yards and cubic feet?
Both measure concrete volume. One cubic yard equals 27 cubic feet. Ready-mix is typically ordered by the yard, while bagged concrete is usually compared by cubic feet per bag.
How many 80 lb bags of concrete equal one cubic yard?
About 45 bags of 80 lb concrete mix equal one cubic yard, assuming a typical yield of around 0.60 cubic feet per bag. Always check the bag label because actual yields vary by brand and mix.
Can I use a generic calculator for footings or bag conversions?
Yes for the underlying math, but the dedicated tools are easier. The footing calculator handles the multiplier for the number of footings automatically. The bag calculator converts a known volume directly into 40, 60, and 80 lb bag counts without needing to enter dimensions again.
How long does it take to mix bagged concrete?
Mixing time depends on the method and the number of bags, but large bag counts add up fast. Once you get into dozens of bags, labor and timing usually become a bigger factor than the price of the bags themselves.
How can I avoid running short on concrete?
Measure carefully, use the right calculator for the project, add a waste factor, and round up before ordering. A small surplus is far cheaper than stopping a pour halfway through and creating a cold joint.
Ready to Estimate Your Project?
Open the calculator that matches your project for instant cubic yard, cubic feet, and bag count estimates.