Construction Calculator
The everyday field math in one place: concrete volume in cubic yards (slabs, footings, and round columns) with pre-mix bag counts, aggregate and fill tonnage by material, and a unit converter covering length, area, volume, and weight. Three tabs, one habit — solid geometry ÷ 27, then convert to whatever the supplier sells by. Free, no login.
Pour
Concrete Needed
Enter dimensions to calculate
How each tab works
Concrete
Solid geometry with a waste allowance on top, delivered in the unit ready-mix is sold by:
slab ft³ = L × W × (thickness ÷ 12) · column ft³ = π r² × height × count · yd³ = ft³ × (1 + waste%) ÷ 27
The waste percentage (default 10%) covers over-excavation, spillage, and uneven subgrade — set it to what your pours actually run. Bag counts are planning figures: they assume ≈0.45 ft³ of yield per 60 lb bag and ≈0.60 ft³ per 80 lb bag, rounded up to whole bags. Check the yield printed on the brand you’re buying — it varies — and past roughly a yard, ready-mix usually beats mixing bags anyway.
Aggregate & fill
The same volume math, then a density conversion to US short tons:
yd³ = L × W × (depth ÷ 12) ÷ 27 · tons = yd³ × density (lb/yd³) ÷ 2,000
The densities are approximate bulk figures — moisture, compaction, and gradation move them meaningfully (wet sand is heavier than dry; compacted base denser than loose). Treat the tonnage as an estimate for ordering and trucking, and confirm the conversion your supplier actually uses — quarries sell by the scale ticket, not by your math.
Unit converter
Exact conversion factors across length, area, volume, and weight — mm to yards, cubic feet to gallons, pounds to tonnes. Enter a value once and see it in every unit of its dimension. These are fixed definitions (27 ft³ per yd³, 231 in³ per US gallon, 2,000 lb per US short ton), so unlike the other two tabs there is nothing to estimate.
Worked example
A 20 × 10 ft shed slab at 4" thick with the default 10% waste, plus a gravel apron:
- Slab volume: 20 × 10 × (4 ÷ 12) = 66.67 ft³; with waste: 66.67 × 1.10 = 73.33 ft³.
- Yards: 73.33 ÷ 27 = 2.72 yd³ — order 3 yards. As bags that would be 123 80-lb bags (73.33 ÷ 0.60, rounded up): ready-mix territory.
- Apron: 40 × 12 ft of dry gravel at 4" deep = 160 ft³ = 5.93 yd³; at 2,835 lb/yd³ that is 5.93 × 2,835 ÷ 2,000 ≈ 8.40 tons.
Reproduce it above: Concrete tab (slab 20 × 10, 4", 10% waste), then Aggregate tab (40 × 12, 4", Gravel (dry)).
Reference: approximate material densities
The bulk densities behind the aggregate tab — approximate values that shift with moisture, compaction, and gradation. Your quarry’s tons-per-yard figure governs the order.
| Material | Density (lb/yd³) | ≈ tons/yd³ |
|---|---|---|
| Gravel (dry) | 2,835 | 1.42 |
| Sand (dry) | 2,700 | 1.35 |
| Crushed stone | 2,700 | 1.35 |
| Road base / crusher run | 2,970 | 1.49 |
| Topsoil | 2,160 | 1.08 |
| Fill dirt | 2,200 | 1.10 |
| Concrete | 4,050 | 2.02 |
| Asphalt (compacted) | 3,960 | 1.98 |
Frequently asked questions
How do I calculate concrete cubic yards?
Concrete volume in cubic yards is (length × width × depth, all in feet) ÷ 27, since a cubic yard is 27 cubic feet. Slab thickness is usually in inches, so divide it by 12 first: a 20 × 10 ft slab at 4 in is 20 × 10 × 0.333 = 66.7 ft³, or 2.47 yd³ before waste. The calculator does the inch-to-foot conversion for you and adds your waste allowance on top.
How many bags of concrete make a cubic yard?
At the yields this calculator assumes — about 0.45 ft³ per 60 lb bag and 0.60 ft³ per 80 lb bag — a full cubic yard (27 ft³) takes roughly 60 of the 60 lb bags or 45 of the 80 lb bags. That is why the tool flags anything at or over 1 yd³: at that volume ready-mix delivery is usually cheaper than bagged concrete, and far easier on your crew.
How much waste factor should I add for concrete?
10% — the calculator default — is a common allowance for slabs and footings poured on grade, where uneven subgrade, over-excavation, and spillage eat volume. Tightly formed work can run less; rough trenched footings can run more. Coming up short mid-pour means a cold joint or a short-load fee, so err high and round up to your supplier’s ordering increment (typically quarter yards).
How do I convert cubic yards of gravel to tons?
Multiply cubic yards by the material’s bulk density in pounds per cubic yard, then divide by 2,000 for US short tons. Dry gravel runs around 2,835 lb/yd³ (≈1.4 tons per yard) and road base / crusher run around 2,970 lb/yd³ (≈1.5 tons per yard) — the approximate densities this calculator uses. Bulk density moves with moisture, compaction, and gradation, so treat the tonnage as an estimate and confirm against your supplier’s ticket weights.
Does the aggregate calculator account for compaction?
No — it computes the volume of the box you enter (length × width × depth) and converts it to tons at an approximate bulk density. Base material loses volume when it is compacted, so if the depth you entered is a finished compacted depth, order extra; your supplier or geotech can give a compaction factor for the specific material. Treat the tool’s tonnage as a floor, not a ceiling.
How many cubic feet are in a cubic yard?
27 — a cubic yard is 3 ft × 3 ft × 3 ft. The unit converter tab handles this and the rest of the everyday jobsite conversions: length (mm through yards and meters), area (square inches to acres), volume (cubic inches through cubic meters, including US gallons and liters), and weight (ounces through US tons and metric tonnes).
Method: solid geometry ÷ 27 for cubic yards, with exact unit definitions (231 in³/gal, 2,000 lb/ton) in the converter. The judgment inputs are labeled as such — the waste percentage is yours, bag yields are planning figures to check against the printed bag, and material densities are approximations no supplier is bound by. Concrete quantity is not concrete design: thickness, mix strength, reinforcing, and subbase come from your plans or engineer, and ready-mix minimum-load and short-load fees can matter more than a tenth of a yard either way.
Pair with the Square Footage Calculator to get the area first, the Rebar Weight & Spacing Calculator for the steel in the pour, or the cubic yard calculation chart for the ÷27 method with excavation swell factors.