Question 1

How do I calculate concrete volume?

Accepted Answer

Use shape formulas (slab: L*W*H). Convert cubic feet to cubic yards by dividing by 27.

Question 2

How much waste should I add?

Accepted Answer

Typically 5-10% for simple forms, 10-15% for complex shapes or manual mixing.

Question 3

How many bags do I need?

Accepted Answer

Approx yields: 40-lb ~ 0.30 ft^3, 60-lb ~ 0.45 ft^3, 80-lb ~ 0.60 ft^3 per bag; check your brand.

Question 4

What about rebar or fiber?

Accepted Answer

Reinforcement does not change volume materially but affects mix selection and placement.

Question 5

How thick should a slab be?

Accepted Answer

Common residential slabs are 4 in thick; follow engineer/contractor specs for your application.

Concrete Calculator — Volume & Materials Calculator