Split into rectangles
Break an L-shaped or irregular slab into the fewest rectangular sections, then measure each one in a consistent unit.
Tool Switcher: Concrete Slab
Project toolsTools
Multi-section concrete tool
Concrete Slab Calculator
Split an irregular slab into rectangular sections, then estimate the combined volume, a planning allowance, ready-mix yards, and whole bags from one price per bag.
- Multiple sections
- US and metric units
- Whole-bag total
Multi-section concrete tool
Concrete Slab Calculator
Combine several slab sections, then estimate volume and whole bags.
Methodology
From several sections to one order
Find each section volume
Length × width × thickness gives each section's volume. The rows stay separate until the project totals are combined.
Apply one allowance
The exact total is combined first, then a single planning allowance is applied once rather than per section.
Round up to whole bags
The planned volume is divided by the selected bag yield and rounded up to whole bags for the final purchase.
Worked example
Two sections with a 10% allowance
20 + 4 ft³two section volumes
×1.1010% allowance
=26.4 ft³planned volume
From 26.4 ft³, an 80 lb mix at 0.60 ft³ per bag requires 44 whole bags. Confirm the exact yield on the product label before buying.
Frequently asked questions
A second look at the estimate.
How do I combine several slab sections?
Measure each rectangular section separately, then let the calculator merge the exact volumes before applying one allowance and rounding whole bags up.
Does the allowance apply per section or once?
Once, on the combined total. Applying it per section would overstate the buffer for a single continuous pour.
Which bag size should I choose?
It depends on your project size and how much you want to handle at once. Heavier bags make fewer bags per volume; lighter bags are easier to lift.
Can I enter metric sections?
Yes. Metric mode uses metres for length and width and centimetres for thickness. Switching units preserves the same physical dimensions.
How is the cost estimated?
Enter a price per bag and the calculator multiplies it by the whole-bag count for your selected size. Without a price, no cost is shown.
Sources and limitations
This tool estimates combined slab volume, an optional allowance, and whole-bag quantities. It does not select slab thickness, reinforcement, mix strength, soil preparation, drainage, or structural suitability, and it does not retrieve live prices.
- Sakrete 5000 Plus product details — source for the displayed bag yields.
- NIST volume conversion factors — reference for cubic-foot, yard, and metre conversion.
- How to measure a concrete slab — prepare section measurements before entering them.
- Concrete bag yield guide — check the nominal yields behind each bag size.
- Concrete calculator — use it for a single repeating shape instead.
- Concrete bag calculator — compare whole-bag counts once you have a single volume.
Planning defaults for 50, 60, and 80 lb bags. Yield varies by product and mixing conditions, so the exact product label or data sheet takes priority.
Last reviewed: August 28, 2026