Concrete Calculator (Volume)
Calculate how much concrete you need for slabs, walls, footings, round columns, round slabs, and stairs. Get cubic yards, cubic feet, cubic meters, pre-mix bag counts, ready-mix truck loads, and a downloadable PDF estimate.
Volumes are geometric estimates. Always add waste for spillage and uneven subgrade, and order a little extra rather than running short. For planning purposes only.
| Bag Size | Yield | Bags Needed | Total Weight | Est. Cost |
|---|
Bag counts cover the full — ft³ (waste included). Bag cost uses your bag price scaled per size.
How to use the concrete calculator
Four quick steps turn your measurements into cubic yards, bag counts, and truck loads — no math required on your end.
Pick your pour shape
Slab, wall, square footing, strip footing, round column (Sonotube), round slab, or solid stairs. Each shape asks only for what it needs.
Enter measurements
Type length, width, and thickness in the units shown. Use Quantity to repeat identical pours like several footings.
Add waste & bag size
Set a 5–10% waste allowance for spillage and uneven base, then choose a 40, 60, or 80 lb bag.
Read results & save a PDF
Get yards, feet, meters, bag counts, truck loads, and cost estimates — then download a PDF for the supplier.
How concrete volume is calculated
Every estimate starts from one idea: volume = length × width × thickness, worked in matching units. Here is the exact formula behind each pour shape, all producing cubic feet.
Worked example — a 10×10×4″ patio slab
Volume: 10 × 10 × (4 / 12) = 33.3 cu ft
Cubic yards: 33.3 / 27 = 1.23 cu yd
Cubic meters: 33.3 × 0.0283168 = 0.94 m³
80 lb bags: 33.3 / 0.60 = 56 bags (rounded up)
With 10% waste → order about 1.36 cu yd, or ~56–62 bags.
Concrete estimating charts
Handy lookups for the most common questions — slab sizes, bag yields, and how thick to pour. Figures below exclude waste, so add 5–10% to your final order.
| Slab size | Cubic feet | Cubic yards | 80 lb bags |
|---|---|---|---|
| 8 × 8 ft | 21.3 ft³ | 0.79 yd³ | 36 bags |
| 10 × 10 ft | 33.3 ft³ | 1.23 yd³ | 56 bags |
| 12 × 12 ft | 48.0 ft³ | 1.78 yd³ | 80 bags |
| 12 × 16 ft | 64.0 ft³ | 2.37 yd³ | 107 bags |
| 16 × 16 ft | 85.3 ft³ | 3.16 yd³ | 143 bags |
| 20 × 20 ft | 133.3 ft³ | 4.94 yd³ | ready-mix |
| 24 × 24 ft | 192.0 ft³ | 7.11 yd³ | ready-mix |
Above ~2–3 cubic yards, bagging becomes impractical and ready-mix is usually cheaper and far less labor. At 6″ thick, multiply the cubic-foot and yard figures by 1.5.
| Bag size | Yield | Bags per cu yd | Best for |
|---|---|---|---|
| 40 lb | 0.30 ft³ | 90 bags | Small patches, setting posts |
| 50 lb | 0.375 ft³ | 72 bags | Light repairs, small pads |
| 60 lb | 0.45 ft³ | 60 bags | Footings, easier lifting |
| 80 lb | 0.60 ft³ | 45 bags | Slabs, best value per ft³ |
Bag counts are always rounded up — you can’t buy part of a bag. Yields are typical for standard pre-mix; check your product’s stated yield.
| Application | Typical thickness |
|---|---|
| Patios, walkways, sidewalks | 4 in |
| Standard car driveway | 4–5 in |
| Garage floor, heavy / RV driveway | 5–6 in |
| Shed & equipment pads | 4–6 in |
| Footings & structural slabs | Per code / engineer |
Always follow local building codes and any engineer’s spec for footing depth, slab thickness, and reinforcement.
Everything the calculator works out
One set of measurements gives you every number needed to order confidently — whether you’re mixing bags or booking a truck.
Key figures every pour depends on
Built for anyone ordering concrete
From a weekend patio to a full foundation package, the same calculator scales to the job.
Pouring a patio, shed pad, or fence-post footings and wants the exact bag count for one trip.
- Start from a preset like Patio 10×10×4″
- Compare 60 vs 80 lb bags for lifting
- Let it flag when ready-mix wins
Prices jobs daily and needs a fast, defensible cubic-yard figure with waste built in.
- Enter $/cu yd for instant costing
- Batch identical footings by quantity
- Keep the PDF on file for quotes
Scoping a build and comparing columns, stairs, and slabs to set a materials budget.
- Model each element, then total yards
- Check truck loads for pour-day logistics
- Use cubic meters for metric specs
7 tips for an accurate estimate
Small habits keep your order right the first time and avoid the two classic mistakes: running short, or over-buying pallets you can’t return.
Concrete calculator FAQ
The formulas, conversions, and ordering questions people ask most before a pour.
Volume is length × width × thickness in matching units. For a slab, keep length and width in feet and divide thickness in inches by 12 to get cubic feet. Divide cubic feet by 27 to convert to cubic yards.
Example: A 10 ft × 10 ft slab at 4 inches deep = 10 × 10 × (4/12) = 33.3 cu ft. Dividing by 27 gives 1.23 cubic yards. Always add 5–10% extra for waste.
One cubic yard equals 27 cubic feet. The number of pre-mix bags required depends on the weight class:
• 80 lb bag: ~0.60 cu ft yield (45 bags per cu yd)
• 60 lb bag: ~0.45 cu ft yield (60 bags per cu yd)
• 50 lb bag: ~0.375 cu ft yield (72 bags per cu yd)
• 40 lb bag: ~0.30 cu ft yield (90 bags per cu yd)
Always round up to the next full bag.
The general formula is Volume = Area × Thickness in uniform units.
• Rectangular Slab / Wall: L(ft) × W(ft) × T(in) / 12
• Round Column: π × (Radius in ft)² × Height(ft)
• Round Slab: π × (Radius in ft)² × Thickness(in) / 12
Divide total cubic feet by 27 for cubic yards or multiply by 0.0283168 for cubic meters.
A standard 10 ft × 10 ft patio slab at 4 inches thick requires 33.3 cubic feet, or 1.23 cubic yards. Including a 10% waste factor, order approximately 1.36 cubic yards or ~56 to 62 80-lb bags.
If poured at 6 inches thick for heavier loads, it requires 50 cubic feet = 1.85 cubic yards (approx. 84 80-lb bags before waste).
• 4 inches: Standard for non-structural residential applications including walkways, patios, and light shed pads.
• 4 to 5 inches: Recommended for standard passenger vehicle driveways.
• 5 to 6 inches: Ideal for garage floors, heavy truck driveways, or RV parking pads.
• Structural footings: Dependent on local building codes and soil conditions (typically 8 to 12+ inches).
Job conditions are rarely perfectly flat. Subgrade unevenness, flexible form boards bowing under load, spillage, and residual material left in mixer drums or pump lines consume extra concrete.
Adding a 5% to 10% waste buffer prevents running short during a pour, which can lead to unsightly structural cold joints or costly emergency short-load delivery charges.
Bagged concrete is cost-effective and manageable for small projects under 1 to 2 cubic yards (e.g., fence posts, small repairs, small step footings).
Ready-mix trucks are significantly faster and physically easier for jobs over 2 cubic yards. Most ready-mix suppliers charge a “short-load fee” for deliveries under 4 to 6 cubic yards, so factor delivery fees when making your decision.
There are exactly 27 cubic feet in 1 cubic yard (3 ft long × 3 ft wide × 3 ft deep = 27 cu ft).
To convert cubic feet to cubic yards, divide by 27. To convert cubic yards to cubic feet, multiply by 27.
General Estimating Notice: This calculator provides volume, bag count, and cost estimates based on user input and standard material densities. Actual job site requirements may vary depending on subgrade preparation, formwork stability, aggregate sizes, and regional supplier yields. Always verify structural specs and footing dimensions with local building codes and suppliers prior to ordering.