TradesHow this works
First it works out the volume. Pick your shape, put in the dimensions, and it gives you the cubic yards with a waste allowance added on, because you never place exactly what the math says. Then it answers the question that actually matters on the day: do you buy bags and mix them, or order a ready-mix truck.
That call comes down to size. A small pour is a few bags and an hour with a wheelbarrow. A big pour is dozens of bags, and mixing that many by hand is slow and hard to keep consistent, so a truck is worth the minimum charge. The tool shows both options side by side with the yardage and, if you enter prices, the cost, so the decision is in front of you.
A quick example
A 10 foot by 10 foot slab at 4 inches thick is about 1.35 cubic yards once you add waste. That is around 60 bags of 80 pound mix. Nobody wants to mix 60 bags by hand, so this is a clear ready-mix job. Shrink it to a 3 foot by 3 foot equipment pad and you are down to a handful of bags, and now the truck's minimum charge makes bags the smart choice.
Common questions
How much concrete do I need?
Enter the shape and dimensions of your pour and the tool works out the volume in cubic yards, plus a waste allowance for spillage and uneven ground. A 10 by 10 slab at 4 inches, for example, is about 1.35 cubic yards once you add waste.
When should I order ready-mix instead of mixing bags?
Roughly, under about a third of a yard, bags are simplest. Over about a full yard, ready-mix wins on both cost and effort. In between it is a judgment call, and the tool leans one way or the other based on what you tell it matters most.
How many bags is too many to mix by hand?
There is no hard rule, but past 50 or 60 bags you are looking at a brutal day and it gets hard to keep the mix consistent. At that point a ready-mix truck is almost always the better call, even with the delivery minimum.
Does this design the slab or footing?
No. It works out how much concrete to buy, not how thick the slab should be or how much rebar it needs. Structural sizing should follow the plan or an engineer.
Sources: Volume geometry (evergreen) · Bag yields: standard concrete-mix published values. Engine version 1.0.0. Risk tier 1.