Concrete is mostly stone
About 60–75% of a mix is aggregate (stone/sand). Cement is the glue, but rock carries the bulk and limits shrinkage.
Mix anatomy
Concrete Yardage Calculator — Slabs, Post Holes & Footings
Calculator
Switch units; we’ll convert outputs to both yd³ and m³.
Covers spillage, uneven subgrade, and pump line loss.
Use decimals for inches/centimetres (e.g., 4.5 in → 0.375 ft).
Typical patios/sheds: 4–6 in (100–150 mm). Heavier loads need engineering.
Slab results will appear here.
Footing/trench results will appear here.
Cylinder results will appear here.
Common sonotubes: 8, 10, 12 in (200–300 mm).
Post hole results will appear here.
Results & Bags
Total Volume
—
With Waste
—
Bags (estimate)
—
Choose bag type:
Bag yields are typical; always check your product’s stated yield.
History (this session)
| Item | Volume (yd³) | Volume (m³) | Actions |
|---|---|---|---|
| No items yet. Calculate to add entries. | |||
How this Concrete Calculator Works
Volume = area × thickness. For rectangular slabs we multiply length by width to get area, then multiply by thickness. For trench footings we use total trench length × trench width × depth. For round columns and post holes we use the cylinder formula \(V = \pi r^2 h\). Inputs can be in imperial (feet/inches, cubic yards) or metric (metres/centimetres, cubic metres). We convert internally and display both yd³ and m³ so you can order locally.
Waste / over-order: concrete placement isn’t perfectly efficient. Subgrades aren’t laser-flat, holes cave slightly, and pumps/hoses hold some mix. A conservative 5–10% extra is common for small projects. Larger pours or complex formwork may warrant a different margin—ask your supplier if unsure.
Bag estimates: Bagged premix lists a typical yield (volume after mixing). Popular sizes and typical yields are: 40 lb ≈ 0.30 ft³, 50 lb ≈ 0.375 ft³, 60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³, 90 lb ≈ 0.675 ft³. Metric bags: 20 kg ≈ 0.009 m³, 25 kg ≈ 0.011 m³, 30 kg ≈ 0.013 m³. Brands vary slightly with blend, aggregate, and water content—always order using the yield on your bag or supplier sheet. For ready-mix trucks, most suppliers quote and deliver in cubic metres or cubic yards.
Common thicknesses: garden paths/shed pads are often 75–100 mm (3–4 in); driveways 100–125 mm (4–5 in) with reinforcement and proper base; structural footings and columns should follow engineer/authority guidance. Depth to frost line varies by region—check local code.
Tips: compact a granular base and screed forms to consistent height to reduce waste. If you’re close to a bag boundary, buy one extra—running short is costlier than having a spare. Keep a small project list handy (stepping stones, fence repair) to use leftover mix.
5 Fun Facts about Concrete Yardage
Water changes volume needs
Each extra gallon of water weakens strength and can add ~1% volume. Don’t “soupy” a mix to stretch yardage; it costs strength and durability.
No watery cheat
Forms aren’t perfect
Wavy subgrades, bulged forms, and hose hold-up easily eat 5–10% extra. That’s why pros routinely over-order a touch.
Real-world waste
Temperature matters
Hot weather speeds set; cold slows it. Both can affect finish time and required water reducers/accelerators—schedule pours with the forecast in mind.
Cure timing
Bag yields vary by brand
“80 lb = 0.6 ft³” is typical, not guaranteed. Gravel size and blend shift yield slightly, so always use the printed yield when converting to bag counts.
Check the bag