Concrete Calculator

Concrete volume starts from geometry. Convert every dimension to feet, compute cubic feet, then divide by 27 to get cubic yards (the unit ready-mix plants quote).

Rectangular slabs and walls use length × width × thickness. Cylinders use π × (diameter/2)² × height. Tubes (annulus) subtract the inner cylinder from the outer. Stairs approximate a triangular wedge plus an optional rectangular landing.

Waste is applied as a multiplier: order volume = geometry volume × (1 + waste%). Bag counts divide cubic feet by an assumed bag yield (about 0.6 ft³ per 80 lb bag) and round up.

yd³ = (L_ft × W_ft × T_ft × quantity × (1 + waste)) ÷ 27

How many 80 lb bags equal one cubic yard?

This tool assumes about 0.6 ft³ yield per 80 lb bag (~45 bags per cubic yard). Bag labels and mix design change yield—always round up and confirm with your supplier.

Can I mix feet, inches, and meters in one calculation?

Yes. Each dimension converts internally to feet before volume is computed, so you can enter metric thickness with imperial length, for example.

Should I order exactly what the calculator shows?

Usually no. Add waste (often 5–10%) for spillage, over-excavation, and pump line residue. Ready-mix plants also have minimum load sizes—call ahead.

Is this enough for a structural permit package?

No. Use it for planning and material takeoffs only. Engineered slabs, rebar schedules, PSI specs, and inspections still require licensed professionals and approved drawings.

How do I convert inches of thickness into the volume formula?

Divide inches by 12 to get feet (4 in = 0.333 ft), then multiply length × width × thickness in feet. The calculator does this conversion for you when you pick the inch unit on a field.

Does the weight estimate include rebar or mesh?

No. Weight is an approximate concrete-only figure from volume × a typical unit weight. Steel, fiber, and formwork are separate takeoffs.

This calculator estimates volume, weight, and premix bag counts for five common pour shapes. Each field has its own unit selector; results include an optional waste allowance.

• Choose a shape tab: Slab / wall, Column, Tube, Curb & gutter, or Stairs.
• Enter every required dimension (length, width, thickness, diameters, riser count, etc.) using ft, in, m, or cm per field.
• Set Quantity for identical pours and Extra waste (%)—5–10% is typical for field spillage and uneven subgrade.
• Tap Calculate to see cubic yards, cubic meters, cubic feet, estimated weight, and rounded-up 80 lb bag counts. Use Clear to reset the active shape.

• Backyard patio, garage slab, or rectangular footing before calling the ready-mix plant.
• Round deck piers, fence-post holes, or sonotube columns where diameter and depth are known.
• Donut-shaped footings, circular slabs, or hollow forms where outer and inner diameters differ.
• Street curb and gutter runs along a driveway or parking apron (verify your municipal cross-section detail).
• Entry or basement stairs when you need a ballpark wedge volume plus an optional top landing platform.

1. Slab: 10 ft long × 10 ft wide × 4 in thick, Quantity 1, 5% waste → about 1.30 yd³ (roughly 59 eighty-pound bags).
2. Column: 2 ft diameter × 4 ft deep, Quantity 1, 5% waste → about 0.49 yd³ (~22 eighty-pound bags).
3. Tube: 4 ft outer diameter, 3 ft inner diameter, 1 ft height for a ring footing—useful when only the annulus is filled.
4. Stairs: 5 risers, 7 in rise, 11 in run, 4 ft width, 3 ft platform depth—tap Calculate after switching to the Stairs tab.

Use this table to decide whether bags or a short-load truck make more sense once you have a yardage estimate.