Example Data Table
| Input | Example Value | Purpose |
|---|---|---|
| Shed size | 12 ft x 20 ft | Sets floor area and perimeter |
| Wall height | 8 ft | Controls stud and wall sheathing needs |
| Stud spacing | 16 in | Calculates wall framing quantity |
| Rafter spacing | 24 in | Estimates roof framing count |
| Waste allowance | 10% | Adds extra material for cuts and mistakes |
Formula Used
Floor area: length x width.
Perimeter: 2 x length plus 2 x width.
Wall sheathing: perimeter x wall height minus door and window area.
Sheet count: required area divided by 32, then multiplied by the waste factor.
Stud count: wall layout studs plus corners and opening support studs.
Rafter length: square root of run squared plus rise squared.
Total cost: lumber cost plus sheathing cost plus roofing cost plus miscellaneous allowance.
How to Use This Calculator
Enter the shed length and width first. Keep 12 and 20 for a standard 12x20 shed. Add wall height, joist spacing, stud spacing, roof pitch, openings, waste, and local prices. Press Calculate to view the estimate. Use CSV or PDF buttons to save the result.
12x20 Shed Lumber Planning Guide
Why lumber planning matters
A 12x20 shed looks simple, yet it uses many connected parts. The floor, walls, roof, plates, headers, and sheathing all depend on the same base dimensions. A small spacing change can affect several rows of material. This calculator helps you prepare a clear starting list before you visit a supplier.
Floor framing basics
The floor is based on a 240 square foot footprint. Joists are counted along the shed length. Rim boards are added around the frame. If you use closer spacing, the joist count increases. Heavy storage, lawn equipment, and workshop use may need stronger floor framing.
Wall framing basics
Wall studs are estimated from the perimeter and stud spacing. Extra studs are added for corners, doors, and windows. Plates are calculated as continuous board length around the walls. A common shed uses a bottom plate and two top plate layers. You can adjust that value for your framing method.
Roof and sheathing basics
The roof estimate uses pitch, shed width, length, overhang, and rafter spacing. A steeper pitch increases rafter length and roof surface area. Sheathing sheets are estimated for the floor, walls, and roof. Standard sheets cover 32 square feet. Door and window openings reduce wall sheet area.
Waste and cost control
Waste is important because sheds require cuts, laps, trimming, and layout corrections. Ten percent is a practical starting point for many basic projects. Complex roofs, many openings, or uneven site conditions may need more. Prices vary by region and grade. Always compare the estimate with your final plan, code needs, and supplier lengths before ordering.
FAQs
1. Is this calculator only for a 12x20 shed?
No. It starts with 12x20 values, but you can change length and width. The formulas will update for different shed sizes.
2. Does the estimate include nails and screws?
It includes a miscellaneous percentage for fasteners and small supplies. You can increase that percentage if your project needs more hardware.
3. Why are door and window sizes included?
Openings reduce wall sheathing area. They also require extra support framing, such as king studs, jack studs, and headers.
4. What sheet size does this use?
It assumes a standard 4x8 sheet. Each sheet covers 32 square feet before waste and trimming are added.
5. What roof style does the calculator assume?
It assumes a simple gable roof. The rafter calculation uses half the shed width, roof pitch, and overhang.
6. Should I order exactly this amount?
Use this as a planning estimate. Final orders should match your drawings, local code, lumber lengths, and supplier recommendations.
7. Why is waste allowance important?
Waste covers cuts, mistakes, damaged boards, layout changes, and unusable offcuts. A higher waste value gives a safer order list.
8. Can I download the estimate?
Yes. After entering your values, use the CSV or PDF button to download the calculated material and cost summary.