How do I calculate concrete for footings?

Treat each footing run as a rectangular strip: length × width × depth. Use the footing shape preset and enter strip dimensions in feet and inches.

How many 80 lb concrete bags do I need?

Divide your volume in cubic feet by the bag yield (80 lb ≈ 0.60 ft³ per bag), add your waste factor, then round up. Our calculator does this live — e.g. a 12×10×4 in slab with 10% waste needs 74 bags.

Should I buy bags or ready-mix?

Small jobs under ~1 yd³ are usually cheaper and easier with bags. Larger slabs and driveways are ordered by the cubic yard from a ready-mix supplier. We show both bag count and order-ready yards.

Concrete Footing Calculator

Footings and foundation strips use the same rectangular volume as a slab — length × width × depth. Switch to the footing shape and enter your trench dimensions.

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Dimensions

Shape

Units

Length (ft)

Width (ft)

Thickness (in)

Number of identical pours

Spillage & Waste (10%)Includes extra so you don't run short

Bag size

Using a pump truck?

Adds 0.5 yd³ to fill the priming lines

Price per bag ($, optional)

Price per yd³ ($, optional)

Result

74 bags (80 lb)

1.6296 yd³ with 10% waste · order 1.75 yd³ ready-mix

How we calculated it

12 ft × 10 ft × 4 in ÷ 12 = 40.00 ft³
+10% waste = 44.00 ft³
44.00 ft³ ÷ 27 = 1.6296 yd³

Yield based on Quikrete/Sakrete published data: 0.60 ft³ per 80 lb bag. Formula: L × W × (T/12) ÷ 27 = yd³. Full methodology

Plan the rest of your project

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Footings and foundation strips use the same rectangular volume as a slab — length × width × depth. Switch to the footing shape and enter your trench dimensions.

Frequently asked questions

How do I calculate concrete for footings?: Treat each footing run as a rectangular strip: length × width × depth. Use the footing shape preset and enter strip dimensions in feet and inches.
How many 80 lb concrete bags do I need?: Divide your volume in cubic feet by the bag yield (80 lb ≈ 0.60 ft³ per bag), add your waste factor, then round up. Our calculator does this live — e.g. a 12×10×4 in slab with 10% waste needs 74 bags.
Should I buy bags or ready-mix?: Small jobs under ~1 yd³ are usually cheaper and easier with bags. Larger slabs and driveways are ordered by the cubic yard from a ready-mix supplier. We show both bag count and order-ready yards.

Frequently asked questions

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