How do you calculate how much concrete you need?

Calculate volume in cubic yards, add waste, then decide bags vs ready-mix. Example: a 12 × 12 patio at 4 inches = 1.78 cu yd; with 10% waste order about 2.0 cu yd (~90 of the 80 lb bags).

How to calculate concrete yards?

Use cubic yards = sq ft × thickness (inches) ÷ 324. For 500 sq ft at 4 inches: 500 × 4 ÷ 324 = 6.17 cubic yards. Add 5–10% for waste.

How to calculate cubic yards of concrete?

Convert thickness to feet (÷12), multiply L × W × T, divide by 27. Or use sq ft × inches ÷ 324. Always add waste before ordering.

How do I calculate yards of concrete?

Same formula as cubic yards. Measure the pour area, convert inches to feet, divide cubic feet by 27. Round up to the next tenth of a yard for ready-mix tickets.

How to calculate concrete yardage?

Yardage = volume in cubic yards after waste. Base yardage = L × W × T_ft ÷ 27; order yardage = base × 1.05 to 1.10 for most slabs.

How to calculate concrete for a slab?

Slab yards = length × width × thickness (ft) ÷ 27. A 10 × 10 slab at 4 inches needs 1.23 cu yd (~1.35 with 10% waste). Use 4 inches for many patios; 4–6 inches for driveways.

How do I use a concrete slab calculator?

Enter length, width, and thickness (often 4 in). The calculator returns cubic yards and bag counts. Add waste, then compare bagged cost vs ready-mix delivery minimums.

How do I use a concrete pad calculator?

A concrete pad uses the same slab math. Measure the pad footprint and thickness. Example: 8 × 10 shed pad at 4 inches = 0.99 cu yd (~1.1 with waste).

How many bags of concrete do I need?

Divide order cubic feet by bag yield: 80 lb ≈ 0.60 cu ft (45 bags/cu yd), 60 lb ≈ 0.45 cu ft (60/cu yd), 40 lb ≈ 0.30 cu ft (90/cu yd). Round up whole bags.

How to calculate bags of concrete?

First get cubic yards, multiply by 27 for cubic feet, then divide by cu ft per bag. For 1.23 cu yd with 80 lb bags: 1.23 × 27 ÷ 0.60 ≈ 55 bags before waste; ~61 with 10% waste.

How much does a concrete slab cost?

Rough planning range is often $4–$15+ per sq ft installed (material + labor), or $120–$200+ per cubic yard for ready-mix material alone. A 200 sq ft 4-inch slab (~2.5 cu yd) might be $300–$500 material before labor.

How do I estimate concrete driveway cost?

Find driveway square footage × thickness for yards, then apply local $/sq ft installed or $/cu yd ready-mix. A 12 × 40 driveway at 5 inches ≈ 7.4 cu yd before waste. Installed driveway pricing is often higher than a simple patio slab.

How do I calculate concrete weight?

Solid concrete is about 150 lb per cubic foot (~4,050 lb or ~2.0 US tons per cubic yard). Multiply cubic yards × 2.0 for approximate tons. Wet mix weight can vary slightly by aggregate and water.

How to calculate concrete from square footage?

You still need thickness. Cubic yards = square feet × thickness (inches) ÷ 324. 300 sq ft at 4 inches = 3.70 cubic yards before waste.

How to calculate concrete for footings?

Footing volume = length × width × depth (all in feet) ÷ 27. A 40-foot footing that is 16 inches wide and 8 inches deep: 40 × 1.333 × 0.667 ÷ 27 ≈ 1.32 cubic yards. Add piers/columns separately.

How to calculate concrete for a Sonotube or post hole?

Use a cylinder: cubic yards = (π × radius² × height in feet) ÷ 27. A 12-inch diameter tube 4 feet tall: π × 0.5² × 4 ÷ 27 ≈ 0.12 cu yd (~6 of the 80 lb bags).

How much concrete for fence posts?

Estimate each post hole as a cylinder (or use bag charts on post packaging). Typical residential posts often need about 1–3 of the 50–80 lb bags each depending on hole size and depth — calculate volume for accuracy.

What is the concrete calculator formula?

Rectangular: cu yd = L × W × T_ft ÷ 27. From square feet: cu yd = sq ft × T_in ÷ 324. Cylinder: cu yd = π × r² × h ÷ 27. Bags ≈ order cu ft ÷ bag yield.

How much gravel under a concrete slab?

Many slabs sit on 4–6 inches of compacted crushed stone. Use the gravel calculator: area × gravel depth ÷ 27 for cubic yards, then add compaction. Example: 10 × 10 slab with 4 inches of gravel ≈ 1.23 cu yd of stone.

Ready-mix or bagged concrete — which should I use?

Under about 1–1.5 cubic yards, bags are often practical. Larger pours usually need ready-mix for speed and consistency. Factor short-load fees when comparing plant quotes.

How to calculate concrete for a patio?

Patio slabs are usually 4 inches. Cubic yards = patio sq ft × 4 ÷ 324. A 12 × 16 patio = 192 × 4 ÷ 324 = 2.37 cu yd (~2.6 with 10% waste).

How do I estimate concrete sidewalk cost?

Find sidewalk sq ft and thickness (often 4 in) for yards, then apply local installed $/sq ft. Material-only is yards × ready-mix $/cu yd. A 4 × 50 sidewalk at 4 in ≈ 2.47 cu yd before waste.

How to calculate concrete for stairs or steps?

Estimate each step as a rectangular volume (run × width × rise) and sum, or model the whole stair as a wedge. Convert cubic feet ÷ 27 for yards. Complex stairs often need a contractor takeoff.

How to calculate concrete for a pier or column?

Use the cylinder formula: cu yd = π × r² × height (ft) ÷ 27. Same method as Sonotube calculators. Add a footing volume separately if the pier sits on a pad.

Concrete Calculator

Q: How to calculate concrete?

Measure length × width × thickness in feet, divide by 27 for cubic yards. Shortcut: square feet × thickness (inches) ÷ 324. Add 5–10% waste, then convert to bags (~45 of the 80 lb bags per cubic yard) or order ready-mix.

Q: How to calculate yards of concrete?

Yards means cubic yards: (L × W × thickness in feet) ÷ 27. A 10 × 20 driveway pad at 4 inches = 2.47 cubic yards before waste.

Free online concrete calculator for slabs, pads, driveways, and footings. Calculate cubic yards, bag counts, yardage from square feet, rough weight, and material cost.

Quick answer

To calculate yards of concrete: cu yd = length × width × thickness (ft) ÷ 27 (or sq ft × inches ÷ 324). A 10 × 10 slab at 4 inches = 1.23 cu yd (~55–61 of the 80 lb bags with waste). Guides: how to calculate yards of concrete, concrete slab cost guide, concrete calculator guide.

Slab / pour areas

Area 1

Length

Width

Thickness

Add waste allowance

Waste %

5–10% is typical for slabs.

Bag size (for bagged mix)

Estimate ready-mix cost

Results

Enter your measurements to see results.

How to calculate concrete (formula)

Cubic yards = Length (ft) × Width (ft) × Thickness (ft) ÷ 27

Cubic yards = Square feet × Thickness (inches) ÷ 324

Cylinder / Sonotube: π × radius² × height (ft) ÷ 27

Bags ≈ (order cu yd × 27) ÷ cu ft per bag

Weight (US tons) ≈ cu yd × 2.0

Full walkthrough with examples: how to calculate yards of concrete.

Concrete slab calculator

A concrete slab calculator is the same volume tool with thickness defaults around 4 inches. Enter length and width (or square footage), set thickness, then add 5–10% waste. Example: 12 × 12 at 4 inches = 1.78 cu yd; order about 2.0 cu yd with waste.

Coverage per cubic yard: about 81 sq ft at 4 inches and 54 sq ft at 6 inches. Cost planning: concrete slab cost calculator guide.

Square feet covered by one cubic yard
Thickness	Sq ft per cubic yard
3 in	108
4 in	81
5 in	65
6 in	54

Concrete pad & driveway calculator

Pads (sheds, HVAC, generators) use slab math at 4 inches unless specs say otherwise. Driveways often need 4–6 inches over a compacted gravel base — calculate concrete and base stone separately with the gravel calculator.

Example driveway: 12 × 40 at 5 inches = 7.41 cu yd before waste (~8.2 cu yd with 10%). That is usually a ready-mix order, not bags.

Concrete bag calculator

After you know order cubic yards, convert to bags. One cubic yard needs about 45 of the 80 lb bags, 60 of the 60 lb bags, or 90 of the 40 lb bags. Bagged mix fits small pads; larger slabs are almost always ready-mix.

Bags per cubic yard
Bag size	Yield	Bags / cu yd
40 lb	0.30 cu ft	90
60 lb	0.45 cu ft	60
80 lb	0.60 cu ft	45