Calculator
Enter your porch details
Choose a unit system, then fill the fields. Use the example button if you want a quick starting point.
Example data table
Sample inputs and outputs
| Example input | Value | Calculated output | Value |
|---|---|---|---|
| Porch size | 12 ft × 14 ft | Area | 168.00 ft² |
| Loads (D/L/S) | 10/40/20 psf | Design uniform load | 78.64 psf |
| Joist spacing | 16 in | Avg joist line load | 108.18 lb/ft |
| Beams / Posts | 2 beams, 6 posts | Max beam line load | 1,119.25 lb/ft |
| Point loads | 400 lb | Total design load | 13,651 lb |
This example assumes a roof is present and uses a 1.10 safety factor.
Replace with your local design loads and actual framing layout.
Formula used
How the calculator estimates loads
- Area: A = L × W
- Screen weight to psf: w_screen(psf) = Screen(lb) ÷ A(ft²)
- Dead load total: D_total = D + w_screen
- Service combo: w = D_total + L + S
- Strength-style combo: w = 1.2D_total + 1.6L + 1.6S
- Safety factor: w_design = w × SF and P_design = P × SF
- Total design load: W_total = (w_design × A) + P_design
- Joist line load (avg): q_joist = (w_design × spacing) + (P_design/joists)/L
- Beam line load (max): assumes evenly spaced beams; interior tributary width equals beam spacing.
- Post load: P_post(avg) = W_total/posts, with a conservative max factor × 1.25.
Important: Real structures can have uneven spans, cantilevers, and concentrated loads.
For final member sizing, confirm with local building guidance or a licensed professional.
How to use
Steps for reliable planning
- Choose a unit system that matches your tape measure.
- Enter porch length, width, and joist spacing.
- Enter dead and live loads based on your build details.
- If the porch has a roof, enable it and add roof/snow load.
- Add estimated screen/railing weight and heavy garden items.
- Set beam and post counts to match your framing layout.
- Pick a load combination and a safety factor for caution.
- Click Calculate Loads, then export CSV or PDF.
For garden projects, point loads often come from large planters, water features, and grills.
Keep heavy items near beams or posts when possible.