Getting from "a number on another page" to an order size
This tool doesn't measure your stair or footing — it takes a volume you already have (or a quick box shape) and turns it into what you can actually hand a supplier.
Get your raw volume
Pull the cubic footage from a project-specific calculator — the Concrete Stairs Calculator, Stair Footing Size Calculator, or a hand measurement — and enter it under "I have a volume." If you only have a rectangular slab or footing, switch to "Calculate from dimensions" instead.
Set your waste allowance
Concrete estimating always adds a buffer over the theoretical volume. 10% is a common default for hand-dug or irregular forms; drop to 5% for a clean, formed pour with a known subgrade.
Check the ready-mix order size
The Ready-Mix Order result is your waste-adjusted volume rounded up to the plant's actual billing increment — this, not the raw calculated number, is what you order.
Compare against bags
For small pours, look at the 60 lb / 80 lb bag counts. Once you're past roughly 40–50 bags, a small ready-mix load or a mini-mix/volumetric truck is usually cheaper and far less labor.
The five formulas behind every result
Nothing on this page is a black box. Here's exactly what runs when you change a number.
Volume from Dimensions
Simple rectangular box volume for a slab, footing or pad. Length and width in feet, depth in inches converted to feet.
Cubic Feet → Cubic Yards
A yard is 3 ft on a side, so a cubic yard is 3×3×3 = 27 cubic feet — the number every ready-mix order is priced against.
Cubic Yards → Metric
0.764555 is the exact defined conversion (1 yard = 0.9144 m, cubed) — not a rounded estimate.
Waste-Adjusted Order
Add the waste allowance first, then round up to the plant's real billing increment — rounding before adding waste can leave you short.
Bag Count Equivalent
Waste-adjusted cubic footage divided by the mixed yield of one bag, rounded up — you can't buy a fraction of a bag.
Walking through a 38.5 ft³ set of steps
Same volume this page loads with by default — the cubic footage a Concrete Stairs Calculator run might return for three exterior steps and a small landing.
Convert the raw volume
38.5 ft³ ÷ 27 = 1.43 yd³. That's the true volume of concrete the steps contain, with zero allowance for spillage or waste.
Add the waste allowance
At the default 10%: 1.43 × 1.10 = 1.57 yd³. This is what you should actually plan to have on site, not the theoretical number from step 1.
Round to the order increment
Rounding 1.57 yd³ up to the nearest 1/4 yard gives a 1.75 yd³ ready-mix order — the plant can't sell you 1.57 yards exactly, so the order always ticks up to the next increment.
Check against the short-load threshold
1.75 yd³ sits well under the typical 3 yd³ short-load minimum, so a short-load fee is likely on a ready-mix delivery. At the same waste-adjusted volume, bagged concrete works out to roughly 57 bags at 80 lb each — worth pricing both options before deciding.
This is exactly why the Ready-Mix Order result can jump a full quarter-yard from a small change in waste % — the rounding step always rounds up, never down, so a waste allowance that pushes you just past an increment boundary costs a full extra 1/4 yard.
Concrete volume conversion factors
These are exact, defined conversions — not rounded estimates.
| From | To | Multiply by | Notes |
|---|---|---|---|
| Cubic feet | Cubic yards | ÷ 27 | Exact — a yard is 3 ft per side. |
| Cubic yards | Cubic meters | × 0.764555 | Exact SI conversion (1 yd = 0.9144 m). |
| Cubic meters | Liters | × 1000 | Exact, by definition. |
| Cubic feet | US gallons | × 7.480519 | Exact (1 US gal = 231 in³). |
| Cubic yards | US gallons | × 201.974 | Exact, derived from the two rows above. |
Bagged concrete yield by size
Mixed yield — not bag weight — is what determines how many bags fill a given volume.
| Bag Size | Mixed Yield | Bags per Cubic Yard | Typical Use |
|---|---|---|---|
| 40 lb | ≈ 0.30 ft³VERIFY | ≈ 90 | Small repairs, post anchoring, patching. |
| 60 lb | ≈ 0.45 ft³VERIFY | ≈ 60 | Most common size for footings and small pads. |
| 80 lb | ≈ 0.60 ft³VERIFY | ≈ 45 | Larger pours where fewer, heavier bags reduce trips. |
Yields are commonly published figures for standard concrete mixes and are consistent across most major bagged-mix brands, but always confirm the number printed on your specific bag before ordering by count — the 60 lb and 80 lb outputs above use these same figures.
Ready-mix vs. bagged: ordering the right way
A correct volume conversion can still lead to the wrong order if it ignores how concrete actually gets sold — this section covers the three things that trip people up.
Why waste comes before rounding
Adding waste after rounding can leave you exactly one increment short on pour day. Always inflate the volume for waste first, then round up to the plant's increment — never the reverse.
Short loads cost more per yard
A truck partially loaded still costs the plant close to a full dispatch, so small orders often carry a flat short-load fee — sometimes larger than the material cost itself. Ask your supplier for their exact threshold before you commit to a delivery.
The bags-vs-truck crossover
Below roughly a third of a yard, bagged concrete is usually cheaper and simpler than paying a short-load fee. Above about half a yard, the labor of mixing 30+ bags by hand typically outweighs any delivery fee — a mini-mix or volumetric truck is worth pricing at that point.
Volumetric (mini-mix) trucks
These trucks mix on site from raw ingredients and only charge for what's actually poured, which sidesteps both the short-load fee and the leftover-concrete problem of a standard dispatch truck — useful for odd, in-between volumes like this example's 1.75 yd³.
These are ordering-stage planning figures based on common industry practice, not a fixed pricing rule — actual thresholds, fees and increments are set entirely by your local supplier.
Common mistakes when converting and ordering concrete
Most concrete-ordering headaches trace back to one of these five errors, not to bad math.
Ordering the exact calculated volume
Zero waste allowance means any spillage, over-excavation or forming imprecision leaves you short mid-pour, with a second truck or a rush bag run to cover the gap.
Confusing cubic feet with square feet
A footing calculator's area output and its volume output look similar at a glance — feeding a square-footage number into this converter as if it were cubic feet silently understates the order.
Not rounding to the plant's real increment
Ordering a precise decimal like 1.57 yd³ instead of the rounded 1.75 yd³ this page recommends often just gets rounded by the plant anyway — better to know the number in advance.
Assuming every bag yields the same volume
Mixed yield varies slightly by brand and mix design. Buying by weight alone, without checking the yield on the bag, can leave a small pour a few bags short.
Not asking about short-load fees upfront
A small order that seems cheap on paper can end up costing more per yard than a full load once the short-load fee lands on the invoice — always ask before scheduling.
Underestimating bag-mixing labor
Forty or fifty 80 lb bags is well over a ton of material to mix by hand or with a small mixer — a volume that looks small in cubic yards can still be a full day's labor in bags.
When to use a concrete volume converter
This tool is the last step before placing an order, across almost any small-to-mid concrete project.
Exterior Steps & Landing
Turning a Concrete Stairs Calculator result into an actual order size.
Deck or Stair Footings
Converting footing volume for one or several posts before a bag or truck order.
Small Patio or Pad
Sizing a slab pour for a shed base, AC pad, or garden patio.
Curb or Ramp Pour
Estimating a short accessibility ramp or curb section.
Retaining Wall Footing
Converting a long, narrow strip footing's volume for ordering.
Garage or Shed Slab
Checking whether a slab pour clears the short-load threshold or needs bags.