Calculator Inputs
Example Data Table
| Scenario | Length | Width | Spacing | Joist size | Joists | Sheets |
|---|---|---|---|---|---|---|
| Garden tool shed | 10 ft | 8 ft | 16 in | 2×6 | 7 | 3 (4×8) |
| Potting shed | 12 ft | 10 ft | 24 in | 2×8 | 6 | 4 (4×8) |
| Compact storage shed | 2.4 m | 1.8 m | 400 mm | 2×6 | 6 | 2 (1220×2440) |
Formula Used
- Joist count = ⌊Run ÷ Spacing⌋ + 1
- Clear joist length = Span − 2×Rim thickness (when between rims)
- Perimeter rim length = 2×(Length + Width)
- Blocking count = (Joist count − 1) × Blocking rows
- Total linear length = Joists + Rim + Blocking
- Total with waste = Total linear length × (1 + Waste% ÷ 100)
- Sheets needed = ⌈Floor area ÷ Sheet area⌉
How to Use This Calculator
- Select your preferred units first.
- Enter shed length and width as outside dimensions.
- Pick joist spacing and the joist size you plan to use.
- Choose joist direction, or keep Auto for shorter spans.
- Set blocking rows and a waste factor for real-world cuts.
- Press Calculate to see results above the form.
- Use Download CSV or Download PDF to save the plan.
Shed floor loads and practical storage
A small garden shed often carries mixed loads: boxed tools, soil bags, a mower, and seasonal items. A conservative planning target is 40 pounds per square foot for light-duty floors, while heavier storage areas benefit from tighter spacing and deeper joists. Use blocking to reduce twist and bounce, especially when spans approach the guidance limit.
Joist spacing impacts material and stiffness
Spacing controls how many joists you need and how stiff the deck feels. Moving from 24-inch to 16-inch spacing increases joist count by roughly 50% across the same run, but it reduces sheet-edge deflection and improves fastener holding. For garden sheds with wheeled equipment, 16-inch spacing typically provides a steadier walking surface.
Span direction and clear span planning
The calculator can span along the shed length or width, or choose the shorter direction automatically. Shorter spans generally allow smaller joists or wider spacing while maintaining stiffness. If joists sit between rim boards, clear span is reduced by twice the rim thickness, slightly lowering lumber length and improving the span check outcome.
Blocking, rim boards, and cutting efficiency
Rim boards form the perimeter and keep joists aligned; their total equals twice the length plus twice the width. Blocking rows add short pieces between joists, strengthening edges and limiting roll. Waste allowance accounts for end trimming, knots, and layout mistakes; 8–15% is typical for simple rectangular frames.
Sheet layout and fastener planning
Floor panels are estimated from shed area divided by sheet area, rounded up. Align sheet edges over joists to reduce squeaks and improve strength. As a baseline, plan fasteners at 6 inches on panel edges and 12 inches in the field. For damp gardens, use treated framing and corrosion-resistant fasteners to reduce early deterioration.
FAQs
1) What spacing should I choose for a garden shed floor?
For general storage, 16 inches often feels stiffer than 24 inches. If you store heavy items or use wheeled equipment, tighter spacing reduces bounce and supports sheet edges better.
2) Does “Auto” span direction change the results?
Yes. Auto selects the shorter shed dimension as the span, which usually reduces clear span and may lower required joist length. It can also improve the simplified span guidance outcome.
3) What does the waste factor cover?
It accounts for trimming ends square, knots, splits, and offcuts from standard stock lengths. Many small shed frames use 8–15% waste. Increase it for complex layouts or limited stock availability.
4) How many blocking rows do I need?
One row at mid-span is common when spans are longer or floors feel springy. Blocking helps keep joists upright and distributes point loads. For short spans, blocking may be optional.
5) Are the span limits code-compliant?
No. The span check is a simplified guidance table for light shed floors and should not replace local requirements. If your shed will carry heavy loads, verify spans with an engineer or local code tables.
6) Can I use metric sizes and still export results?
Yes. Select metric units, enter meters and millimeters, then calculate. The download buttons create CSV and PDF exports with the same unit system shown on screen.