How is volume calculated?

Length × width × thickness (with thickness converted from inches or centimeters into the same unit as length). Waste multiplies that volume before bag math.

When should I order ready-mix instead of bags?

Roughly past one to two cubic yards, delivery often costs less labor than mixing dozens of bags. Use the yardage readout as a tipping-point check.

What yield per bag should I enter?

Read the bag. A common 80 lb US bag yields about 0.6 cubic feet, but high-strength and sand mixes vary. Metric sacks list liters or m³ per bag.

Does this include rebar or forms?

No — only concrete volume. Plan reinforcement, base gravel, and form lumber separately.

Footings or post holes?

For simple rectangular footings the same L×W×D model works. Round sonotubes need πr²h; this page is aimed at rectangular pads and paths.

Pouring a deck footing next?

Size the pads here, then estimate decking with [[deck-material-calculator|Deck material calculator]]. For patio tile on a slab, see [[tile-calculator|Tile calculator]].

Is structural advice included?

No. Thickness, mix design, and reinforcement for load-bearing work need local code guidance or an engineer.

Work out concrete volume and bags to buy

Enter length, width, and thickness for a rectangular pad or path, add a waste percent, and set yield per bag. The tool returns volume, volume with waste, cubic yards (imperial), and bags to buy.

Units

Length (ft)Width (ft)Thickness (in)Waste %Yield per bag (cu ft)

Results

Volume: 33.3333 cu ft

Volume with waste: 36.6667 cu ft

Cubic yards: 1.358

Bags to buy: 62

Formula

Volume = L×W×thickness; Volume with waste = volume × (1 + waste); Bags = ceil(volume with waste ÷ yield per bag)

Worked steps (check these)

Thickness = 4 in → 0.3333 ft
Volume = 10×10×0.3333 = 33.3333 cu ft
Volume with waste = 33.3333 × (1+0.1) = 36.6667 cu ft
Cubic yards = 36.6667 ÷ 27 = 1.358
Bags to buy = ceil(36.6667 ÷ 0.6) = 62

Estimates only — confirm with product labels and a licensed pro. Not a substitute for structural or roofing advice.

Concrete shopping fails in two directions: a short load that sets before the mixer truck can return, or a mountain of leftover bags that harden in the garage. A clear volume with a modest waste percent keeps the pour continuous without betting the budget on guesswork.

Thickness is easy to mistype. Four inches is a common patio thickness; driveways and frost-aware footings may need more. Enter thickness in inches (imperial) or centimeters (metric) — the calculator converts to match length and width before multiplying.

On hot days or long wheelbarrow runs, waste creeps up because material stiffens in the barrow. If helpers are few, favor ready-mix once yardage climbs. After the slab cures, finish surfaces with tile or leave broom-finished as outdoor space beside a deck.

How to estimate concrete

Choose imperial or metric units
Enter length, width, and thickness
Set waste % and yield per bag from the sack
Read volume, yards (imperial), and bags to buy

Why use this concrete calculator

Turns inches of thickness into real cubic volume.
Waste % and bag yield are explicit — no hidden defaults you cannot see.
Shows cubic yards for ready-mix conversations.
Rounds up to whole bags for store runs.
Metric and imperial share the same workflow.

Good for

Shed or AC pad takeoffs
Sidewalk or garden path sections
Small patio slabs before tiling
Comparing bag counts vs a short ready-mix order
Fence post piers approximated as rectangular voids

Common concrete mistakes to avoid

Entering thickness in feet while thinking in inches (4 ft thick is not a patio).
Ignoring waste on rough grade that eats extra mix.
Assuming every 80 lb bag yields 0.6 cu ft without reading the label.
Starting the pour without enough help, then adding water to “save” a stiff batch.
Forgetting base compaction — a soft base makes the slab thicker than planned and short on mix.

Worked concrete examples

Input	Output	Note
10×10 ft pad, 4 in thick, 10% waste, 0.6 cu ft per 80 lb bag	Volume ≈33.33 cu ft; with waste ≈36.67 cu ft ≈1.36 yd³ → 62 bags	V=L×W×D; bags=ceil(V×(1+waste)/yieldPerBag)
10×10 ft, 6 in thick, 10% waste, 0.6 cu ft/bag	Volume 50 cu ft; with waste 55 cu ft ≈2.04 yd³ → 92 bags	Thicker slabs jump bag counts quickly — check whether ready-mix is cheaper
Metric: 3×3 m, 10 cm thick, 10% waste, 0.0125 m³ per bag	Volume 0.9 m³; with waste 0.99 m³ → 80 bags at that yield	Confirm bag yield on the sack; mixes differ by strength and aggregate

Concrete calculator FAQ

How is volume calculated?: Length × width × thickness (with thickness converted from inches or centimeters into the same unit as length). Waste multiplies that volume before bag math.
When should I order ready-mix instead of bags?: Roughly past one to two cubic yards, delivery often costs less labor than mixing dozens of bags. Use the yardage readout as a tipping-point check.
What yield per bag should I enter?: Read the bag. A common 80 lb US bag yields about 0.6 cubic feet, but high-strength and sand mixes vary. Metric sacks list liters or m³ per bag.
Does this include rebar or forms?: No — only concrete volume. Plan reinforcement, base gravel, and form lumber separately.
Footings or post holes?: For simple rectangular footings the same L×W×D model works. Round sonotubes need πr²h; this page is aimed at rectangular pads and paths.
Pouring a deck footing next?: Size the pads here, then estimate decking with Deck material calculator. For patio tile on a slab, see Tile calculator.
Is structural advice included?: No. Thickness, mix design, and reinforcement for load-bearing work need local code guidance or an engineer.