ConstruclyticHome
WorkspaceNew takeoff

Concrete how-to · updated

Ready-mix or bags: when each makes sense

There is no universal one-yard cost break-even. Compare the full cost of each supply method for the same waste-adjusted pour, then check whether access, mixing capacity and the placement window make it practical.

Feroz SheikhWritten by Feroz Sheikh · founderCalculator suite checked Oct 3, 2026.

Open the concrete bag calculator Concrete planning guide

Worked example — 12 ft circle, no waste

A 12 ft diameter, 4 in circular pad with 0% waste contains about 1.40 yd³ net. The slab calculator rounds the ready-mix planning order up to 1.50 yd³ in 0.25 yd³ steps; confirm the supplier’s actual increment and billing minimum. For bagged supply, the unrounded net volume gives 126 of 40 lb bags at 0.30 ft³ each or 63 of 80 lb bags at 0.60 ft³ each. Do not use the rounded truck order to calculate bags or add both alternatives together. Replace those planning yields with the selected product label, then compare complete local quotes.

Concrete bag calculator: measurement diagram. Measure each dimension in the unit shown beside its input. Thickness is separate from plan dimensions.
Measure each dimension in the unit shown beside its input. Thickness is separate from plan dimensions. View image

What a bag actually yields

Yield is printed on the bag, not implied by the weight. Construclytic’s planning yields are 0.30 ft³ for 40 lb, 0.375 ft³ for 50 lb, 0.45 ft³ for 60 lb and 0.60 ft³ for 80 lb. Real yield moves with slump and aggregate, so counts always round up.

Post holes and sonotubes are the classic bag job: a few 80 lb sacks per hole, mixed next to the pier. A 10 × 10 patio at 4 in is already ~1.2 yd³ net — 55-plus 80 lb bags before waste.

Compare two complete local quotes

For bags, multiply the whole-bag count by the price of the exact product. Add any store delivery, mixer hire, mixing labour and handling costs for this job. For ready-mix, ask the supplier for the billable quantity and the complete delivered price, including any minimum-order, short-load, access, waiting or placement charges. Do not add a charge again if it is already included in the quote.

Use the concrete cost calculator linked below for a quoted ready-mix quantity and unit rate; record other charges separately in the estimate. If the supplier bills a minimum quantity, distinguish that billable quantity from the volume to place. Keep tax and labour scope consistent between the two quotes. Confirm the specified mix, access and placement plan before treating either total as an option.

Do it in order

  1. Calculate net volume from the real shape, then apply waste.
  2. Price the whole-bag quantity and the supplier’s billable ready-mix quantity separately. Add the quoted delivery, equipment and labour costs to each option without double-counting.
  3. Replace the default yield with the selected product’s labelled yield before you buy.

Planning boundary

Bag counts are planning yields. They are not a mix design, a PSI guarantee or a labour-hour estimate.

Can I mix bag brands in one pour?

Not if you care about colour or set. Stay on one product and one water window.

Does bag size change the cubic yards?

No. Volume is volume. Bag size only changes how many sacks you lift.

What about volumetric mix trucks?

They meter on site. You still start from a waste-adjusted volume; you do not skip the takeoff.