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Concrete Calculator

Everyday

Calculate cubic yards, cubic metres, and concrete bag count for slabs, columns, or tube forms. Covers both 60 lb and 80 lb bag sizes instantly.

Reviewed by the thecalcu.com team · Last updated June 21, 2026

Shape
ft
ft
in
Volume
—
cubic yards
— m³  |  — cu ft
Concrete Bags Needed
80 lb Bags
—
(0.6 cu ft each)
60 lb Bags
—
(0.45 cu ft each)
Add 5–10% extra for spillage and uneven sub-base. Order by the nearest half-yard from your ready-mix supplier.

What is a Concrete?

A concrete calculator estimates the volume of concrete needed for any pour, slabs, driveways, walkways, footings, deck columns, and Sonotube forms, and converts that volume into the number of premixed bags you'll need to buy. Doing this by hand means juggling conversions between cubic inches, cubic feet, and cubic yards while accounting for pour shape, which is exactly how projects end up with too much leftover mix or a frustrating mid-pour run to the hardware store.

Concrete comes in two common forms: dry premix bags (typically 40, 60, and 80 lb) and ready-mix delivered by truck, priced by the cubic yard. Bags make sense for small DIY jobs, a garden path, a few deck footings, a small patio slab. Ready-mix delivery pays off for anything bigger, like a full driveway or a house foundation, where the per-yard cost drops sharply despite the delivery minimum.

This calculator handles three pour shapes: rectangular slabs and footings (the most common by far), solid cylindrical columns and piers, and hollow tube forms where an inner void reduces total volume. For each shape, it returns the volume in cubic yards (the standard US ordering unit), cubic meters (for suppliers who quote metric), and bag counts for both 60 lb and 80 lb premix.

If you're also planning the finished surface, the Square Footage Calculator and Tile Calculator help size the room and figure out tile quantities that go over a concrete base.

Why Use a Concrete Calculator?

Avoid an expensive miscalculation. Concrete can't be returned once it's mixed and delivered. Underestimate and you're paying for a second delivery with its own minimum charge; overestimate and you're stuck disposing of hardened leftover mix. Getting the number right up front avoids both outcomes.

Skip the manual unit conversion. Ready-mix suppliers often quote in cubic yards or cubic meters, while hardware stores sell bags by weight. This calculator shows all three simultaneously so you can compare a delivery quote against the bagged-concrete option without doing the math yourself.

Handle shape-specific formulas correctly. A column pour doesn't follow the same arithmetic as a slab. The calculator applies the π × r² formula for circular cross-sections and subtracts the inner void for hollow tubes, so you're not trying to remember geometry formulas mid-project.

Get a precise shopping list. Knowing you need exactly 23 bags of 80 lb concrete means one trip to the store with the right number in hand, no guessing, no over-buying, no second trip.

Who Should Use This Calculator?

Homeowners and DIY builders tackling weekend projects, garden paths, patio slabs, deck footings, small retaining walls, can figure out bag quantities in seconds and head to the store with an exact shopping list.

Contractors and site supervisors can use it for quick estimates during early planning, before a detailed engineering spec is available, especially for footings and deck or fence post pours.

Renovation crews pouring a leveling screed under new flooring can calculate exactly how much concrete to order, avoiding the common mistake of underestimating depth across an uneven sub-floor.

First-time homeowners working with a contractor can cross-check the volume a contractor quotes against their own calculation before signing off on a bid.

How to use this Concrete calculator

  1. Select the Shape, choose Slab / Footing for flat horizontal pours, Column / Pier for solid cylindrical pours (deck footings, structural columns), or Tube / Hollow for cylindrical pours with a void (Sonotube-style forms).
  2. Enter dimensions, for a slab, enter length, width, and depth or thickness in feet and inches. For a column, enter the outer diameter and height. For a tube, also enter the inner diameter (the void). The calculator only shows the fields relevant to your chosen shape.
  3. Read the outputs, check cubic yards for comparing against a ready-mix quote, and the bag counts for a hardware store shopping list. Round up to the nearest whole bag and add 10% for waste and sub-base irregularity.
  4. Decide on bags vs. delivery, for volumes under about 1 cubic yard (~0.76 m³), bags are usually the practical choice. Above that, compare the total cost of bags against ready-mix delivery, including the delivery minimum.

Formula & Methodology

Slab Volume:
Volume (ft³) = Length (ft) × Width (ft) × Depth (in) ÷ 12
Volume (yd³) = Volume (ft³) ÷ 27

Column Volume:
Volume (ft³) = π × (Diameter / 2)² × Height (ft)

Tube Volume:
Volume (ft³) = π × ((Outer Diameter / 2)² − (Inner Diameter / 2)²) × Height (ft)

Cubic yards to cubic meters: yd³ × 0.7646 = m³

Bags per cubic yard: an 80 lb bag covers 0.60 ft³, so bags = ceil(Volume ft³ ÷ 0.60). A 60 lb bag covers 0.45 ft³, so bags = ceil(Volume ft³ ÷ 0.45).

Worked example: A homeowner in Denver wants to pour a driveway apron 12 ft × 8 ft × 4 inches thick.

- Depth in feet = 4 ÷ 12 = 0.333 ft
- Volume = 12 × 8 × 0.333 = 32 ft³
- Cubic yards = 32 ÷ 27 = 1.19 yd³
- Cubic meters = 1.19 × 0.7646 = 0.91 m³
- 80 lb bags = ceil(32 ÷ 0.60) = ceil(53.3) = 54 bags
- 60 lb bags = ceil(32 ÷ 0.45) = ceil(71.1) = 72 bags

Adding 10% for waste: order 60 bags of 80 lb, or 80 bags of 60 lb. Alternatively, at this volume, a single ready-mix delivery (most suppliers' minimum load runs about 1 cubic yard) is often the more economical route.

Quick Reference

Pour size Best option
Under ~1 cubic yard Bagged premix
1–5 cubic yards Compare bags vs. ready-mix delivery cost
Over 5 cubic yards Ready-mix delivery

Once you know your concrete volume, use the Square Footage Calculator to plan the finished surface area, or the BTU Calculator if the same project includes sizing a garage or workshop's heating and cooling.

Frequently Asked Questions

For a rectangular slab, multiply length (ft) × width (ft) × thickness (ft), then divide by 27 to convert cubic feet into cubic yards. The Concrete Calculator does this automatically, enter your dimensions and it returns cubic yards, bag counts, and cubic meters instantly.
One 80 lb bag of premixed concrete covers roughly 0.6 cubic feet, and since a cubic yard holds 27 cubic feet, you'll need about 45 bags of 80 lb concrete to fill it. For 60 lb bags, which cover about 0.45 cubic feet each, plan on roughly 60 bags per cubic yard.
Standard practice is ordering 5–10% more than the calculated volume to cover spillage, uneven sub-grade thickness, and minor formwork leaks. This calculator gives you the exact calculated volume, add 10% to that figure before placing an order with a ready-mix supplier.
A slab or footing is a flat, horizontal pour with uniform depth, used for driveways, patios, and foundations. A column is a solid vertical cylinder, like a deck footing or a structural pier. A tube is a hollow cylinder, like a Sonotube form, where you specify both the outer diameter and the inner void diameter.
Volume = π × radius² × height. This calculator handles it automatically once you select 'Column', just enter the outer diameter and height and it computes the circular cross-section volume. When calculating by hand, remember to halve the diameter to get radius before squaring it.
Slab: Volume (cu ft) = Length (ft) × Width (ft) × Depth (ft). Column: Volume = π × (Diameter/2)² × Height. Tube: Volume = π × ((Outer Diameter/2)² − (Inner Diameter/2)²) × Height. Divide any result by 27 to get cubic yards, or multiply by 0.0283 to get cubic meters.
Convert 4 inches to feet: 4 ÷ 12 = 0.333 ft. Volume = 10 × 10 × 0.333 = 33.3 cubic feet = 1.23 cubic yards. That's roughly 56 bags of 80 lb premixed concrete, or 74 bags of 60 lb. Add a 10% waste buffer and you're looking at about 62 bags (80 lb) or 82 bags (60 lb).
For pours under about 1 cubic yard (roughly 45 bags of 80 lb premix), bagged concrete from a hardware store is usually more practical and cost-effective. For anything bigger, driveways, large slabs, foundations, ready-mix truck delivery is faster, more consistent, and works out cheaper per cubic yard despite the minimum-load delivery fee.
A garden path or light-duty walkway is fine at 3–4 inches. A standard residential driveway needs 4–5 inches. Anything carrying heavy vehicles or serving as a structural slab typically needs 6 inches or more. Local frost depth, soil conditions, and rebar reinforcement also affect the recommended thickness, check with a structural engineer for load-bearing work.
One cubic meter equals roughly 1.308 cubic yards or 35.3 cubic feet, and takes about 59 bags of 80 lb premix to fill. Some ready-mix suppliers, especially outside the US, quote and price by the cubic meter, so having that conversion on hand makes it easier to compare quotes apples-to-apples.
Yes, use the 'Slab / Footing' mode and enter your footing dimensions. For strip footings that run along a wall, you may need to calculate section by section and add the volumes together. For any structural foundation work, always have a structural engineer verify your depth and rebar spec, this calculator gives volume, not load-bearing design.
Also known as
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