This concrete calculator estimates pour volume in cubic yards from length, width, and depth. Use it to plan slabs, pads, and simple rectangular pours before you call a ready-mix plant or count bags.
Ready-mix is sold by the cubic yard. Bagged mix is sold by weight with coverage charts. Starting from volume keeps both purchasing paths honest.
Who should use this concrete calculator
DIY builders and contractors use it for shed pads, sidewalk sections, and rectangular footings. If the shape is an L or has thickened edges, break it into rectangles and add the yards.
Structural design, rebar schedules, and mix strength are separate from volume. Confirm those with your plans or engineer.
Municipal inspectors may require a stated thickness and compressive strength. Meet those requirements first, then use this calculator to translate thickness into yards. Strength and volume are related only through the design you already chose.
Home centers sometimes sell project kits with suggested bag counts. Cross-check those suggestions with your measured length, width, and depth so marketing coverage charts do not silently assume a thinner slab.
How to use the concrete calculator
- Enter length and width in feet for the pour footprint.
- Enter depth (thickness) in inches.
- Read cubic yards from the result.
- Add waste for spillage and uneven subgrade, often about 5 to 10 percent.
- Convert to bags using the coverage on your bag label if you are not ordering ready-mix.
How concrete volume is calculated
Depth in inches is divided by 12 to get feet. Area times depth gives cubic feet. Divide by 27 for cubic yards.
Cubic yards = length (ft) × width (ft) × (depth (in) ÷ 12) ÷ 27
That matches the live MultiCalify concrete tool inputs: length (ft), width (ft), and depth (inches).
Worked slab example
A 10 ft × 10 ft slab at 4 inches thick:
Depth = 4 ÷ 12 = 0.333 ft.
Cubic feet = 10 × 10 × 0.333 ≈ 33.3 ft³.
Cubic yards = 33.3 ÷ 27 ≈ 1.235 yd³.
With 10 percent waste, plan about 1.36 yd³. Ready-mix minimums may force a larger order, so confirm plant rules.
| Input | Value |
|---|---|
| Length | 10 ft |
| Width | 10 ft |
| Depth | 4 in |
| Volume | ~1.235 yd³ |
| With 10% waste | ~1.36 yd³ |
Bags versus ready-mix
Bag labels list yield at a stated thickness. Divide your cubic feet by the bag yield in cubic feet and round up. Small pads often favor bags. Larger slabs usually favor ready-mix once labor and consistency matter.
Include delivery fees, short-load fees, and wait time when comparing quotes. A slightly higher unit price can win if fees are lower.
Subgrade, thickness, and waste
Soft or uneven subgrade increases volume. Measure thickness after forms are set, not only from the plan sketch. Order a little extra rather than finishing short mid-pour.
Footings, steps, and multi-thickness pours
A slab with thickened edges is not one flat rectangle. Calculate the thin field and the thicker edge beams separately, then add cubic yards. Steps and stem walls also need their own length × width × depth math.
If a pour includes piers, treat each pier as a cylinder approximation only when you accept that estimate quality. For critical structural work, follow engineered quantities rather than a quick rectangle model.
Weather, placement, and finishing waste
Hot, windy days can force faster placement and more discarded mix at the chute. Pump lines hold volume that never reaches the forms. Ask the supplier how they handle leftover and whether short loads carry fees so your waste percent matches the placement method.
Cold weather and hot weather mixes can change how you schedule, but they do not change the geometric volume. Keep volume planning separate from mix design and admixture choices.
Control joints, reinforcement, and finishing crew timing
Rebar, wire mesh, and fiber do not change cubic yards of concrete, but they change labor sequencing. Order volume so the truck arrives after forms and steel are ready. Waiting time fees can exceed the cost of a slightly larger load that finishes cleanly.
Colored or stamped finishes may require a single continuous pour for appearance. That pushes you toward one delivery sized with honest waste rather than two short loads that create a cold joint.
For DIY bag mixes, stage water, tools, and helpers before you open bags. Bag yield assumes proper water ratios. Over-watering weakens the slab and can change how far a bag spreads.
Driveway aprons that connect to public sidewalks may need specific thickness and fiber requirements. Check local rules, then size yards to those thicknesses. A calculator cannot waive a municipal minimum.
If you are pouring in sections with cold joints, estimate each day’s pour separately so truck sizing matches crew speed. Ordering one giant load for a slow DIY crew wastes concrete and money.
Common concrete calculator mistakes
- Entering depth in feet when the field expects inches
- Ignoring thickened edges or footings
- Ordering exact yards with no waste
- Mixing bag yield assumptions across brands
- Forgetting short-load fees on small ready-mix orders
Limitations
This estimates rectangular volume only. It does not size reinforcement, specify PSI, or account for pump line waste. Confirm final orders with your supplier and project plans.
Bags versus ready mix
Small footings and post holes often suit bags. Slabs and long pours usually need ready mix once yardage climbs. Convert bag yield to cubic yards so both quotes use one unit.
Overage and waste
Order a little extra for spillage and uneven subgrade. Running short mid pour is expensive. Confirm whether your quote is loose or placed volume.
Shape notes
Rectangles are length times width times depth. For cylinders such as post holes, use the circular area formula then convert to cubic yards outside this simple slab style tool if needed.
For related unit and percent checks while you plan materials, try the unit converter or the percentage calculator.