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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.

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 required for any pour — slabs, driveways, footpaths, columns, fence post holes, and tube forms — and converts that volume into the number of pre-mixed concrete bags you need to buy. Working without a calculator, estimating concrete volume requires converting between cubic inches, cubic feet, and cubic yards while accounting for the shape of the pour, which leads to costly over-ordering or frustrating under-ordering mid-job.

Concrete is sold in two common formats in India and internationally: pre-mixed dry bags (available in 40 lb, 60 lb, and 80 lb sizes) and ready-mix by the cubic metre (or cubic yard), delivered by truck. For small DIY projects such as a garden path, fence posts, or a small patio, bags are more practical. For larger pours — a house foundation, a full driveway, or a large slab — ready-mix delivery is more economical.

The Concrete Calculator handles three pour shapes: rectangular slabs and footings (the most common), solid cylindrical columns and piers, and hollow tube forms where an inner void reduces the total concrete volume. For each shape, it outputs the volume in cubic yards (the standard commercial ordering unit internationally), cubic metres (the standard in India), and the bag count for both 60 lb and 80 lb premixed bags.

If you are also planning the floor surface area, the Square Footage Calculator and Tile Calculator can help you size the room and calculate tile quantities above the concrete base.

How to use this Concrete calculator

  1. Select the Shape — choose Slab / Footing for flat horizontal pours, Column / Pier for solid cylindrical pours (fence posts, structural columns), or Tube / Hollow for cylindrical pours with a void (cardboard tube forms used for piers).
  2. Enter dimensions — for a slab, enter the 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 conditionally shows only the relevant fields.
  3. Read the outputs — note the cubic yards figure for ready-mix comparison and the bag counts for hardware store planning. Round up to the nearest whole bag and add 10% extra to account for waste and sub-base irregularity.
  4. Plan your purchase or delivery — for volumes under 1 cubic yard (~0.76 m³), bags are practical. For anything over 1 cubic yard, compare the total cost of bags versus ready-mix delivery including the delivery minimum charge.

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 metres: yd³ × 0.7646 = m³

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

Worked example: A homeowner in Pune wants to pour a concrete 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 metres = 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% wastage: order 60 bags of 80 lb or 80 bags of 60 lb. Alternatively, one ready-mix delivery of 1 m³ (with the supplier's minimum being 0.5 m³ or 1 m³) is more economical for this volume.
Frequently Asked Questions
How do I calculate cubic yards of concrete needed?
For a rectangular slab, multiply length (ft) × width (ft) × thickness (ft), then divide by 27 to convert cubic feet to cubic yards. The Concrete Calculator does this automatically — just enter your dimensions and it outputs cubic yards, bags, and cubic metres instantly.
How many 80 lb bags of concrete make a cubic yard?
One 80 lb bag of premixed concrete covers approximately 0.6 cubic feet. Since there are 27 cubic feet in a cubic yard, you need roughly 45 bags of 80 lb concrete per cubic yard. For 60 lb bags, which cover about 0.45 cubic feet each, you need approximately 60 bags per cubic yard.
How much extra concrete should I order for wastage?
Standard practice is to order 5–10% more concrete than calculated to account for spillage, variations in sub-grade thickness, and minor formwork leaks. The Concrete Calculator gives the exact calculated volume — add 10% to that figure when placing your order to a ready-mix supplier.
What is the difference between a concrete slab, column, and tube pour?
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 of concrete, such as a fence post or pier. A tube is a hollow cylinder (like a cardboard tube form) where you specify both the outer diameter and the inner void diameter.
How do I calculate concrete for a circular column?
Volume = π × radius² × height. The Concrete Calculator handles this automatically when you select 'Column' — enter the outer diameter and height and it computes the circular cross-section volume. Remember to convert diameter to radius by dividing by 2 before doing manual calculations.
What is the formula for calculating concrete volume?
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 for cubic metres.
How much concrete do I need for a 10×10 ft slab at 4 inches deep?
Convert 4 inches to feet: 4 ÷ 12 = 0.333 ft. Volume = 10 × 10 × 0.333 = 33.3 cubic feet = 1.23 cubic yards. That equals approximately 56 bags of 80 lb premixed concrete or 74 bags of 60 lb. With a 10% wastage buffer, order 62 bags (80 lb) or 82 bags (60 lb).
Should I use premix concrete bags or ready-mix truck delivery?
For small pours under 1 cubic yard (about 45 bags of 80 lb premix), bagged concrete from a hardware store is usually more cost-effective and practical. For larger pours — driveways, large slabs, or foundations — ready-mix delivery is faster, more consistent in quality, and ultimately more economical per cubic yard despite the minimum delivery charge.
How thick should a concrete slab be in India?
For a garden pathway or light-duty area, 3–4 inches (75–100 mm) is adequate. A standard residential driveway needs 4–5 inches (100–125 mm). Heavy vehicles or structural slabs require 6 inches (150 mm) or more. Local soil conditions and reinforcement used also affect the recommended thickness — consult an engineer for structural work.
What does cubic metres of concrete mean, and how does it relate to bags?
One cubic metre equals approximately 1.308 cubic yards or 35.3 cubic feet. A cubic metre of concrete requires roughly 59 bags of 80 lb premix. Ready-mix concrete in India is typically ordered and priced per cubic metre (often written as m³), so knowing your volume in cubic metres makes it easier to get an accurate quote from a supplier.
Can I use this calculator for poured concrete footings for a house?
Yes — use the 'Slab / Footing' mode and enter the footing dimensions. For strip footings along a wall, you may need to calculate one section at a time and add the volumes. For deep footings or structural foundations, always verify your calculations with a structural engineer, as load-bearing requirements affect both depth and concrete grade (mix ratio) rather than just volume.

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