Shed Concrete Slab Calculator (Volume, Bags & Cost)

Q: How much waste should I allow?

5–10% is common to allow for spillage, uneven subgrade and over‑excavation.

Q: What slab thickness should I use?

Many shed slabs use 100–125 mm (4–5 in) with a compacted base, but check local code and soil conditions; some sites require a thickened edge.

Q: Are bag yields accurate?

Bagged concrete yields vary. Use the labeled yield on your product for best results.

Plan a shed slab in minutes. Enter slab dimensions and thickness, optionally add a thickened perimeter, and the tool estimates total concrete volume in m³ and yd³, converts to bag counts, and estimates costs. Metric & imperial supported.

How to use

Choose units (Metric or Imperial).
Enter length × width and slab thickness.
(Optional) Toggle Thickened edge and set width/depth if your slab has a perimeter beam.
Set waste % and, if using bags, edit the yield per bag and price.
Click Calculate. You’ll see total volume, bags required, truck/bag cost, perimeter length, area and optional base gravel.

Worked example

Metric: Shed 3.0 m × 2.4 m, slab thickness 100 mm, thickened edge 300 mm wide to 200 mm depth, waste 8%.

Slab volume: 3.0 × 2.4 × 0.10 = 0.720 m³
Edge beam extra: perimeter 10.8 m × 0.30 × (0.20−0.10) = 0.324 m³
Total (with 8% waste): (0.720+0.324) × 1.08 = 1.127 m³ (≈ 1.47 yd³)

Shed slab calculator

FAQs

How much waste should I allow?

Concrete volume usually includes 5–10% extra for spillage, uneven subgrade and over‑excavation.

What slab thickness should I use?

Common shed slabs range from 100–125 mm (4–5 in) with a compacted base. Check your local code and soil conditions; some sites require a thickened edge.

Are bag yields accurate?

Bagged concrete yields vary by brand and mix. Enter the labeled yield from your product (per bag) for best results.