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
Perimeter posts needed
18
Wall siding area (sq ft)
1,680
Roof area (with pitch) (sq ft)
1,380
Estimated post cost
$720
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter barn length (ft).
- 2Enter barn width (ft).
- 3Enter wall height (ft).
- 4Enter post spacing (ft).
- 5Enter price per post ($).
- 6Read your perimeter posts needed on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
A 30x40 pole barn is a popular size for a workshop, hobby garage, or equipment storage building. This calculator estimates the number of posts around the perimeter at a given spacing, the wall siding area, and the roof area based on your wall height and roof pitch, giving you a shopping list starting point and a rough material cost.
Worked example
Using the values the calculator loads with:
Inputs
- Barn length: 40 ft
- Barn width: 30 ft
- Wall height: 12 ft
- Post spacing: 8 ft
- Price per post: 40 $
Results
- Perimeter posts needed: 18
- Wall siding area (sq ft): 1,680
- Roof area (with pitch) (sq ft): 1,380
- Estimated post cost: $720
What each field means
Inputs
- Barn length (ft)
- The barn length used in the calculation, measured in ft. Starts at 40 ft so you have a working example on load.
- Barn width (ft)
- The barn width used in the calculation, measured in ft. Starts at 30 ft so you have a working example on load.
- Wall height (ft)
- The wall height used in the calculation, measured in ft. Starts at 12 ft so you have a working example on load. Accepted range: 8–20 ft.
- Post spacing (ft)
- The post spacing used in the calculation, measured in ft. Starts at 8 ft so you have a working example on load. Accepted range: 4–12 ft.
- Price per post ($)
- The price per post used in the calculation, measured in $. Starts at 40 $ so you have a working example on load.
Results
- Perimeter posts 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.
- Wall siding area (sq ft)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Roof area (with pitch) (sq ft)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated post cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How far apart should pole barn posts be spaced?
8 feet on center is a common default for light to moderate loads; wider spans need larger posts or additional engineering to handle snow and wind loads.
How tall should a 30x40 pole barn be?
12 feet is typical for equipment or a workshop with a loft; go higher if you need to fit an RV or tall machinery inside.
Does this calculator include the concrete floor?
No, use a dedicated slab calculator for the floor — this tool covers the post frame, wall siding, and roof area only.
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). 30x40 Pole Barn Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/30x40-pole-barn-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/30x40-pole-barn-calculator" target="_blank" rel="noopener">30x40 Pole Barn Calculator — RevenueLab</a> (2026).</p>
Source: [30x40 Pole Barn Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/30x40-pole-barn-calculator) (2026).