Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
80-lb bags needed
20
Equivalent ready-mix yards
0.43
Estimated bag cost
$130
Total cubic feet
10.7
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter pad length (ft).
- 2Enter pad width (ft).
- 3Enter thickness (in).
- 4Enter waste factor (%).
- 5Enter price per 80-lb bag ($).
- 6Read your 80-lb bags needed on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
A 4x8 pad is a common size for a small storage shed, generator, or AC condenser base. This calculator defaults to 4 inches thick, small enough that most people mix it themselves with 80-lb bags rather than ordering ready-mix, so both the bag count and the ready-mix cubic yardage are shown side by side along with total material cost.
Worked example
Using the values the calculator loads with:
Inputs
- Pad length: 8 ft
- Pad width: 4 ft
- Thickness: 4 in
- Waste factor: 10 %
- Price per 80-lb bag: 6.5 $
Results
- 80-lb bags needed: 20
- Equivalent ready-mix yards: 0.43
- Estimated bag cost: $130
- Total cubic feet: 10.7
What each field means
Inputs
- Pad length (ft)
- The pad length used in the calculation, measured in ft. Starts at 8 ft so you have a working example on load.
- Pad width (ft)
- The pad width used in the calculation, measured in ft. Starts at 4 ft so you have a working example on load.
- Thickness (in)
- The thickness used in the calculation, measured in in. Starts at 4 in so you have a working example on load. Accepted range: 2–12 in.
- Waste factor (%)
- The waste factor used in the calculation, measured in %. Starts at 10 % so you have a working example on load. Accepted range: 0–30 %.
- Price per 80-lb bag ($)
- The price per 80-lb bag used in the calculation, measured in $. Starts at 6.5 $ so you have a working example on load.
Results
- 80-lb bags needed
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Equivalent ready-mix yards
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated bag cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total cubic feet
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How many bags of concrete for a 4x8 shed pad?
At 4 inches thick with 10% waste, about 20 bags of 80-lb concrete mix — well within DIY mixing range for a weekend project.
Do I need gravel under a 4x8 shed pad?
Yes, 3-4 inches of compacted gravel base is standard under any shed slab to improve drainage and reduce frost heave, in addition to the concrete volume calculated here.
Is a slab necessary for a small shed, or can I use pavers?
A poured pad gives the most stable, level, rot-resistant base, but a well-compacted paver or gravel pad works fine for lightweight sheds under 100 square feet in areas without heavy frost.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). 4x8 Shed Pad Concrete Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/4x8-shed-pad-concrete-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/4x8-shed-pad-concrete-calculator" target="_blank" rel="noopener">4x8 Shed Pad Concrete Calculator — RevenueLab</a> (2026).</p>
Source: [4x8 Shed Pad Concrete Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/4x8-shed-pad-concrete-calculator) (2026).