Free tool
Concrete Volume Calculator
Convert slab dimensions into cubic yards with overage, plus equivalent 80 lb bag counts for small pours. The same volume math used by Drevanto's certified concrete assembly.
Result
Results updated.
| Concrete incl. overage | 2.72cu yd |
|---|---|
| 60 lb bags (alternative) | 163bags |
| 80 lb bags (alternative) | 123bags |
Formula
- cubic yards = (length × width × thickness ÷ 12) ÷ 27 × (1 + overage)
- 60 lb bags = ceil(cubic feet incl. overage ÷ 0.45 cu ft per bag)
- 80 lb bags = ceil(cubic feet incl. overage ÷ 0.60 cu ft per bag)
Assumptions
- 0.45 cu ft yield per 60 lb bag and 0.60 cu ft per 80 lb bag (common manufacturer yields).
- 10% overage is a common allowance for uneven subgrade and spillage.
What this does not cover
- Reinforcement, forms, base preparation, and finish are not estimated.
- Large pours are usually more economical as ready-mix — bag counts are shown for comparison only.
Planning aid only — not a quote. Quantities use documented rules of thumb; verify against your plans, local codes, site conditions, and real supplier pricing before ordering or bidding.
Methodology
Concrete volume is length × width × thickness (thickness converted from inches to feet), giving cubic feet; divide by 27 for cubic yards. Overage — 10% is a common starting point — covers subgrade irregularities, spillage, and the last wheelbarrow. Bag equivalents use 0.6 cubic feet per 80 lb bag, which is the yield printed on standard concrete mix packaging. Ready-mix is typically ordered in quarter-yard increments; check your supplier.
Worked example: 20 × 10 ft slab at 4 in. thick, 10% overage
- Volume = 20 × 10 × (4 ÷ 12) = 66.7 cu ft
- With overage = 66.7 × 1.1 = 73.3 cu ft ÷ 27 = 2.72 cu yd
- Bag equivalent = ceil(73.3 ÷ 0.6) = 123 × 80 lb bags
Frequently asked questions
When should I order ready-mix instead of bags?
As a rough threshold, anything over about one cubic yard is cheaper and more consistent from a truck. Bagged pours also struggle to finish before the mix sets on warm days.
Does thickness include the base?
No. Enter the concrete thickness only. Gravel base depth is a separate takeoff — same volume math with your base depth.
Can Drevanto estimate a full concrete scope?
Yes — concrete flatwork is one of the 26 certified Instant assemblies, producing an editable estimate with materials, labor hours, and readiness checks.
Certified benchmark · 2026-08-21
In 520 certified profile-mode generations across 26 supported Instant assemblies on Windows (profile/AOT) and an Android API 36 emulator, supported jobs became editable estimates in a median of 0.028 seconds (rounded); the measured 95th percentile was 48.008 milliseconds (approximately 0.048 seconds), with 0 generative-AI provider calls.
- median, supported jobs
- 0.028 sec
- certified generations
- 520
- supported assemblies
- 26
- failures · 0 AI provider calls
- 0
Certified supported jobs only. Editable output; contractor pricing and field verification remain in control. Full methodology and results
See it run on your own jobs
The private Drevanto beta is the real, editable product — not a website demo. Apply, and we will follow up by email.