Check before acting
- Measure depth at several points when the subgrade is uneven.
- Use mixed yield from the bag or supplier data, not bag weight by itself.
- Confirm access, batch capacity and placement time before choosing bags versus ready-mix.
Home & DIY
Concrete Calculator
Calculate slab volume, order volume, ready-mix quantity, bag count, and budget in metric or US customary units.
01
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DECISION GUIDE
How to use this result in a real decision.
What order quantity covers the slab dimensions and a realistic allowance for site variation? Calculate finished volume from consistent units, add waste for depth variation and spillage, then convert the order volume using the supplier's stated bag yield or ready-mix unit.
WORKED EXAMPLE
A 10 ft × 10 ft slab, 4 inches deep
- Inputs
- 100 sq ft area, 4-inch depth, 8% waste and 0.60 cu ft yield per bag.
- Calculated result
- Finished volume is about 33.33 cu ft; the order volume is 36 cu ft. At 0.60 cu ft per bag, the estimate is 60 bags.
- Decision meaning
- A small depth error affects every square foot. Check the formed depth and subgrade before relying on the purchase count.
Not included automatically
- Structural design, reinforcement, joints and code requirements
- Base material, forms, pumping, delivery minimums and short-load fees
- Weather, curing method and site-specific mix specifications
How to use it
A better estimate in three steps.
- 01
Measure the slab length, width, and finished depth.
- 02
Add waste for uneven subgrade, spillage, and form variation.
- 03
Use your bag's stated yield for the closest estimate.
Core formula
The math behind the result.
Concrete volume = length × width × depth; order volume = volume × (1 + waste rate)Questions
Useful before you decide.
How much extra concrete is sensible?
For a regular slab, 5–10% is common. Irregular excavation or uncertain depth can require more.
Why does bag yield matter?
Bag weight alone does not guarantee the same mixed volume. Use the yield printed by the manufacturer.
Can I use this for structural work?
Use it for preliminary quantity planning only. Structural dimensions and mix specifications should come from the project design and local requirements.