The calculator above gives you the volume in cubic yards, cubic feet, and cubic meters for six pour types: slabs, footings, columns, tube piers, steps, and curb and gutter. It also shows bag count for 40, 60, and 80 lb bags, includes a 10% waste buffer, and estimates total cost. This guide explains the math behind each result and the decisions you need to make before ordering material.
Table of Contents
- How to use this concrete calculator
- Slab calculations
- Footing calculations
- Column and tube pier calculations
- Step calculations
- Curb and gutter calculations
- Bags vs. ready-mix: which to use
- PSI guide by project type
- Concrete cost in 2026
- Tips before you pour
- Frequently asked questions
How to Use This Concrete Calculator
Select your pour type from the six tabs at the top. Each tab shows the relevant dimension inputs and a live SVG diagram that updates as you type.
Enter dimensions in feet and inches (imperial) or meters and centimeters (metric). Use the unit toggle to switch. The calculator keeps all three volume outputs, cubic yards, cubic feet, and cubic meters, visible at once regardless of which unit you input.
Set the quantity field to combine identical pours. For 12 fence post holes with the same diameter and depth, enter 12. The calculator multiplies the single-unit volume, adds 10% waste, then shows total bags and cost across all 12 holes.
Select your bag size. The default is 60 lb. Change it to 40 lb or 80 lb and the bag count updates immediately. Bag yields shown are standard: 0.30 cubic feet for 40 lb, 0.45 cubic feet for 60 lb, and 0.60 cubic feet for 80 lb.
Slab Calculations
The slab formula is: length (ft) x width (ft) x thickness (in) / 12 = cubic feet. Divide by 27 for cubic yards.
A fast field shortcut for 4-inch slabs: divide the square footage by 81 to get cubic yards directly. This works because 4 inches is 1/3 of a foot, and 27 / 0.333 = 81.
Standard slab thicknesses:
- Patios and sidewalks: 4 inches
- Garage floors (passenger vehicles): 4 inches
- Driveways (standard): 5 inches
- Driveways (heavy trucks or RVs): 6 to 8 inches
- Pole barn and shop floors: 6 inches
Add control joints every 10 feet in both directions for any slab larger than 100 square feet. Without them, shrinkage cracks appear randomly within the first year.
Footing Calculations
The footing formula is the same as a slab: length x width x depth = cubic feet. The difference is that depth is entered in feet, not inches, since footings are typically deeper than slabs.
Footings must extend below the local frost line per IRC Section R403.1.4. Frost depth ranges from near zero in Florida to 60 inches or more in northern Minnesota and Maine. Your local building department publishes the minimum required footing depth for your area. Do not guess. A footing that stops above the frost line will heave when the soil freezes, cracking walls and misaligning openings above.
Typical residential footing widths from IRC Table R403.1(1):
- One-story structure, standard soil: 12 inches wide, 6 to 8 inches thick
- Two-story structure, standard soil: 15 inches wide, 8 inches thick
- Three-story structure, standard soil: 23 inches wide, 10 inches thick
These are minimums. Your engineer or local code may require more. Always pull a permit and schedule a footing inspection before pouring. Most jurisdictions require the inspector to physically measure depth before the pour is approved.
Column and Tube Pier Calculations
For rectangular columns, the formula is: width x depth x height = cubic feet.
For tube piers (round forms like Sonotube), the formula is: pi x radius squared x height = cubic feet. The calculator uses this exact formula when you enter diameter. A 10-inch diameter tube that is 4 feet deep needs 0.218 cubic feet per tube, or about 0.008 cubic yards.
Pour tube forms in one continuous operation. If you stop mid-pour and the first lift begins to set before you continue, you create a cold joint. Cold joints are weaker than monolithic concrete and fail under lateral loads. For deck piers and fence posts, this matters.
Square columns need rebar on all four corners for structural applications. Use a 3000 PSI mix minimum. Allow 7 full days of cure time before loading a column.
Step Calculations
Concrete steps use a staircase volume formula. Each step sits on top of all the steps below it. The volume formula is: width x rise x run x (number of steps x (number of steps + 1) / 2) = cubic feet.
For a 4-foot wide stairway with 4 steps, a 7-inch rise, and an 11-inch run: 4 x (7/12) x (11/12) x (4 x 5 / 2) = 4 x 0.583 x 0.917 x 10 = 21.4 cubic feet, or 0.79 cubic yards before waste.
Steps need a 3500 PSI mix at minimum. Slope each tread 1/8 inch per foot toward the front edge so water drains off. Finish with a broom texture for traction. Add 15% to 20% waste for steps due to the complexity of forming.
Curb and Gutter Calculations
The curb and gutter formula calculates the cross-sectional area and multiplies by length. Cross-section area = (curb width x curb height) + (gutter width x gutter thickness). Then multiply by length to get cubic feet.
The diagram shows a cross-section view rather than a 3D box because the cross-section is the measurement that matters most for ordering material. Length just scales it up.
Road applications typically use a 4000 PSI mix. Add control joints every 10 feet to manage shrinkage cracking.
Bags vs. Ready-Mix: Which to Use
The crossover point is 1 cubic yard.
Under 1 cubic yard, bags from the home improvement store are practical. An 80 lb bag yields 0.60 cubic feet. One cubic yard (27 cubic feet) needs 45 bags. At roughly $6 per bag, that comes to about $270 per cubic yard in material cost alone. You also avoid minimum order fees and short-load charges.
Over 1 cubic yard, ready-mix wins on both cost and quality. Ready-mix concrete costs $160 to $195 per cubic yard delivered in 2026, with the 2024 national average at $179.89 per cubic yard per NRMCA data. That is less than the per-yard cost of bags, and you get computerized batching that produces more consistent concrete than hand-mixing.
Watch for short-load fees. Short-load fees run $40 to $60 per cubic yard for orders below the truck’s typical capacity of 10 cubic yards. If you need 2 cubic yards, add those fees to your per-yard cost before comparing to bags. A volumetric mixer (a truck that mixes on site and charges only for what you use) avoids this problem entirely for small pours.
One cubic yard of concrete weighs about 4,000 pounds. Mixing that by hand takes 3 to 8 hours with a portable mixer versus 30 minutes for a ready-mix truck to pour and finish. For anything over 1 yard, your time has value too.
PSI Guide by Project Type
PSI measures compressive strength at 28 days. Higher PSI means more cement in the mix, better durability, and better freeze-thaw resistance. These are the standard minimums:
- 2500 PSI: Non-structural interior slabs with no exposure to freezing
- 3000 PSI: Footings, foundations, residential sidewalks, patios in mild climates
- 3500 PSI: Driveways, steps, exterior slabs in cold climates
- 4000 PSI: Driveways in freeze-thaw climates, garage floors, curb and gutter
- 4500 to 5000 PSI: Commercial slabs, heavy vehicle areas, structural columns
In areas exposed to deicing salts, the IRC requires air-entrained concrete with 5% to 7% air content by volume. Air entrainment protects against freeze-thaw damage. Specify this when ordering ready-mix. Bagged concrete labeled “crack resistant” or “high strength” often includes air entrainment, but confirm on the bag label.
Concrete Cost in 2026
Enter your material and labor costs per cubic yard in the cost bar below the calculator. The total updates as you type and applies to the waste-adjusted volume.
2026 ready-mix pricing by order size:
- Full truckload (10 yards): $125 to $165 per cubic yard delivered
- Short load (under 10 yards): add $40 to $60 per cubic yard in fees
- Bagged concrete (80 lb): roughly $270 to $290 per cubic yard in material
Installation labor for flatwork (pouring, screeding, finishing) runs $5 to $8 per square foot in most U.S. markets. Stamped or decorative concrete pushes to $12 to $18 per square foot due to specialized finishing time. Short-load charges for orders under 8 to 10 yards add $50 to $150 per yard above the base rate. Get that number from your supplier before finalizing your order.
Concrete prices rose 3% to 6% in 2025 and 2026 due to cement supply constraints and fuel surcharges. Always get quotes from two or three local suppliers and confirm whether the quoted price includes delivery or not.
Tips Before You Pour
Order 10% more than your calculation. Uneven subgrades, form expansion, and spillage all consume material. The calculator includes this buffer already. Do not subtract it.
Pour in one continuous operation. If your pour is interrupted long enough for the first batch to begin setting, you create a cold joint. Cold joints are the leading cause of early concrete failure in residential work. Schedule your pour so the truck is on site and ready before you start.
Do not add extra water to extend workability. Extra water lowers PSI and increases shrinkage. If the mix is too stiff, ask the driver to add a plasticizer at the truck. Plasticizers improve flow without weakening the concrete.
Cure properly. Concrete gains strength by staying wet, not by drying out. Cover fresh slabs with plastic sheeting or spray with curing compound immediately after finishing. Keep them moist for at least 7 days. Concrete reaches design strength at 28 days.
Compact the subgrade. Concrete does not bridge soft spots. Any void under a slab causes cracking within the first freeze-thaw cycle. Compact fill material in 6-inch lifts and test with a penetrometer or simple walk test before pouring.
Call 811 before you dig. Any footing or pier deeper than 12 inches requires a utility locate call at least two business days before digging. This is law in every U.S. state.
Frequently Asked Questions
How do I calculate how much concrete I need?
Multiply length by width by thickness to get cubic feet. Divide by 27 to convert to cubic yards. Add 10% for waste. For a 4-inch slab, divide the square footage by 81 to get cubic yards directly. The calculator does this automatically for all six pour types.
How many bags of concrete do I need for a 10×10 slab?
A 10×10 foot slab at 4 inches thick is 33.3 cubic feet, or 1.23 cubic yards. With 10% waste you need 1.36 cubic yards, or 36.7 cubic feet. That equals about 61 bags of 80 lb concrete or 82 bags of 60 lb concrete. At this volume, comparing the bag cost against a short-load ready-mix delivery is worth doing before you buy.
When should I use bags instead of ready-mix concrete?
Use bags for projects under 1 cubic yard. Above that, ready-mix is cheaper per yard and saves significant labor. Bagged concrete works out to roughly $270 to $290 per cubic yard, while ready-mix runs $125 to $175 per cubic yard delivered. The break-even depends on short-load fees from your local supplier.
How thick should a concrete slab be?
Use 4 inches for patios, sidewalks, and garage floors under standard loads. Use 5 to 6 inches for driveways. Use 6 to 8 inches for driveways that will support heavy trucks or RVs. Increase thickness before increasing PSI when you need more load capacity.
How deep do footings need to be?
Footings must extend below the local frost line per IRC Section R403.1.4. Frost depth ranges from near zero in Florida to 60 inches or more in northern Minnesota. Check with your local building department for the required minimum before you dig. A footing above the frost line will heave as the soil freezes and thaws.
