Calculator Inputs
Enter dimensions, spacing, and optional pricing. Results update after submit.
Example Data Table
Sample inputs and a typical output snapshot for reference.
| Scenario | Length (ft) | Width (ft) | Posts | Beam plies | Rafter spacing (in) | Slat spacing (in) | Waste (%) | Output highlights |
|---|---|---|---|---|---|---|---|---|
| Backyard shade pergola | 16 | 12 | 6x6 | 2 | 24 | 12 | 10 | Cut list, linear feet, board feet, and optional cost. |
Formulas Used
1) Overhang conversions
Convert inches to feet:
overhang_ft = overhang_in / 12
2) Member run lengths
beam_run_ft = length_ft + 2 × beam_overhang_ft
rafter_span_ft = width_ft + 2 × rafter_overhang_ft
slat_run_ft = length_ft + 2 × slat_overhang_ft
3) Rafter and slat counts (spacing)
rafter_count = floor(length_ft / (rafter_spacing_in/12)) + 1
slat_rows = floor(rafter_span_ft / (slat_spacing_in/12)) + 1
4) Waste allowance
pieces_with_waste = ceil(pieces × (1 + waste_pct/100))
5) Board feet
Using actual thickness and width (inches):
board_feet = (thickness_in × width_in × length_ft) / 12
How to Use This Calculator
- Measure the pergola’s overall length and width in feet.
- Set post height and embed depth based on your footing design.
- Enter post spacing, then choose beam plies for the main runs.
- Add overhangs to match your desired look and water drip line.
- Choose rafter and slat spacing to control shade and stiffness.
- Select nominal sizes, or enter custom actual dimensions if needed.
- Pick stock lengths to minimize splices and reduce waste.
- Add optional prices and hardware for a rough material estimate.
- Press calculate, then download the CSV or PDF for purchasing.
Always confirm structural spans, wind uplift, and local code requirements.
Professional Notes on Pergola Lumber Planning
1) Start with a clear geometry takeoff
A reliable takeoff begins with the outside footprint. Record length and width in feet, then add your planned overhangs. For example, a 16×12 pergola with 12‑inch beam overhangs becomes an 18‑foot beam run, which immediately affects board counts and splice risk.
2) Post layout drives stability and cost
Post spacing along the long sides is a major cost lever. Many residential builds use 6–10 ft spacing depending on beam size and site exposure. This calculator estimates posts per long side using spacing, then applies waste so you can purchase full-length stock confidently.
3) Beam plies reflect real framing practice
Beams commonly use double plies (two boards fastened together) to increase capacity and stiffness. Entering 2 plies doubles the main run members per side. If a beam run exceeds your selected stock length, the tool flags that splices may be required and counts extra boards accordingly.
4) Rafter spacing affects shade and feel
Typical rafter spacing is 16 or 24 inches on-center. Tighter spacing increases visual density and can reduce bounce under wind. The rafter count is based on length and spacing, then expanded with waste. A 16‑ft length at 24 inches typically yields 9 rafters before waste.
5) Slat spacing controls coverage and material
Slats (purlins) add shade and style. Common spacing ranges from 6–12 inches depending on desired coverage. This calculator creates slat rows across the rafter span and assigns each row a run length along the pergola. Longer runs may need multiple boards per row if stock is shorter.
6) Board‑foot totals support purchasing and quoting
Board feet help compare suppliers even when pricing is inconsistent by piece. The tool uses actual thickness and width to compute board feet: (T×W×L)/12. This matters because nominal sizes differ from actual sizes; for instance, 2×6 is commonly 1.5×5.5 inches.
7) Waste is not optional on a jobsite
A realistic waste allowance covers cuts, checking, knots, and layout changes. Many crews carry 8–15% for pergola work. If you are doing angled tails, decorative notches, or selecting appearance-grade pieces, consider the higher end to avoid costly mid-project runs.
8) Use the output as a field-ready cut list
After calculating, download the CSV for estimating or procurement and the PDF for site coordination. The cut list shows piece length, quantities, stock lengths, and board counts. Always verify uplift, lateral bracing, and local fastening schedules before building.
FAQs
1) Does this calculator design the structure for code loads?
No. It produces a material takeoff from your inputs. Confirm beam sizing, footing depth, uplift restraint, and connectors with local requirements or an engineer, especially in high-wind or seismic areas.
2) Why can board counts increase when runs exceed stock length?
When a run is longer than a stock board, you must splice. The calculator estimates boards per run using ceiling(run ÷ stock). Stagger splices between plies and follow fastening guidance for joints.
3) What is a good starting point for post spacing?
Many pergolas use 8 ft spacing, then adjust based on beam size, site wind, and aesthetic needs. Shorter spacing reduces beam demands and deflection but increases post, footing, and hardware costs.
4) How should I choose rafter and slat spacing?
Use 16–24 inches for rafters and 6–12 inches for slats as a common baseline. Tighter spacing increases shade and stiffness. Wider spacing reduces material but can look sparse and cast less shadow.
5) Why does the tool use actual dimensions for board feet?
Board feet are volume-based, so actual thickness and width are required. Nominal sizes are names, not measurements. Using actual dimensions improves consistency when comparing quotes and tracking consumption.
6) Should I include embed depth if I’m using post bases?
If posts sit on surface-mounted bases, set embed depth to 0. If posts are embedded in concrete, include the below-grade portion so post stock length and total wood volume are not underestimated.
7) Can I estimate costs if my supplier prices by linear foot?
Yes. Use the total linear feet for each category and apply your rate externally, or convert to a per-board price. Board-foot totals also help translate between pricing models when quotes differ.