How much concrete should you order?

1. Split the project into measurable pours

Measure the inside dimensions of each form or excavation at the size you expect to fill. A slab, thickened edge, footing and post hole may need different formulas. Keep them separate, then add the volumes. The multi-pour calculator handles rectangular and round areas in one estimate.

For irregular slabs, divide the outline into simple rectangles that do not overlap. Measure each rectangle, calculate its volume and sum them. For sloped or uneven excavations, take several depth readings; a single shallow reading can understate the volume.

2. Check the exact volume before adding extra

A 10 ft × 10 ft slab at 4 in thick has 10 × 10 × (4 ÷ 12) = 33.33 cubic feet. Dividing by 27 gives 1.23 cubic yards. This is the geometric volume. A 10% allowance makes the planning order 36.67 cubic feet, or 1.36 cubic yards. The allowance is an input you can change, not a universal rule.

If a footing trench is wider than the plan or a slab base is low in places, remeasure it. A percentage cannot reliably correct a known dimensional error.

3. Compare bags and ready-mix using the same volume

Concrete bags are purchased by whole units. At an approximate yield of 0.60 cubic feet per 80 lb bag, the example above needs 36.67 ÷ 0.60 = 61.11, rounded up to 62 bags. That is 4,960 lb of dry bagged material to move and mix. The bag calculator also supports 40 and 60 lb bags.

Ready-mix is ordered by volume. Ask local suppliers about their minimum order, short-load fee, delivery access and order increments. Compare the delivered quote with the bag cost and the work involved; this site does not assume one purchasing method is always cheaper.

4. Confirm the details with your supplier

• Give the measured dimensions, number of pours and target order volume.
• Confirm the actual yield on the bag or product sheet; specialty mixes can differ.
• Ask about delivery minimums, truck access, unloading time and any extra fees.
• Use the mix specification in the plans; this calculator does not select strength or design reinforcement.
• Recheck dimensions after forms and excavation are complete, before placing the final order.

Common measurement errors

Mixing inches and feet without conversion, counting overlapping areas twice, using outside form dimensions instead of fill dimensions, and rounding each small pour before adding them can all skew an estimate. pourmeasure sums unrounded geometric volumes and rounds only the displayed result and final bag count. The methodology page lists conversion factors and source yields.