Calculator Inputs
Formula Used
This calculator estimates framing members for a rectangular pergola with two beam lines, repeated rafters, and repeated top slats.
- Posts per side:
ceil(length ÷ max post spacing) + 1 - Total posts:
posts per side × 2 - Beam segments:
(posts per side - 1) × 2 × beam plies - Beam linear feet:
2 × beam plies × pergola length - Rafter count:
ceil(length ÷ rafter spacing) + 1 - Rafter piece length:
width + 2 × overhang - Slat count:
ceil(width ÷ slat spacing) + 1 - Slat piece length:
length + 2 × overhang - Board feet:
(nominal thickness × nominal width × linear feet) ÷ 12 - Waste-adjusted value:
base quantity × (1 + waste%) - Estimated cost:
adjusted board feet × price per board foot
Stock piece counts are estimated from waste-adjusted linear feet divided by your selected stock length, then rounded up.
How to Use This Calculator
- Enter the pergola length, width, and finished height.
- Set the post allowance for embedment or anchoring detail.
- Choose the maximum post spacing you want to allow.
- Enter rafter spacing, top slat spacing, and side overhang.
- Select member sizes for posts, beams, rafters, and slats.
- Enter stock lengths you expect to buy from your supplier.
- Add waste percentage and a price per board foot.
- Press calculate to see quantities, board feet, stock pieces, cost, and a member graph.
Example Data Table
| Example | Length (ft) | Width (ft) | Height (ft) | Post Spacing (ft) | Rafter Spacing (in) | Slat Spacing (in) | Beam Plies | Overhang (ft) | Waste (%) | Adj. Board Feet |
|---|---|---|---|---|---|---|---|---|---|---|
| Sample Pergola A | 16 | 12 | 8 | 8 | 16 | 12 | 2 | 1 | 10 | 753.87 |
| Sample Pergola B | 20 | 14 | 9 | 10 | 18 | 14 | 3 | 1.5 | 12 | Varies by selected sizes |
Frequently Asked Questions
1) What does this pergola lumber calculator estimate?
It estimates posts, beams, rafters, top slats, design linear feet, adjusted board feet, stock pieces, and an approximate lumber cost using your selected sizes and waste factor.
2) Does it include hardware and fasteners?
No. This version focuses on lumber quantities and lumber cost only. Bolts, anchors, brackets, stain, roofing, and concrete should be estimated separately.
3) Why is there a post allowance input?
Post allowance covers embedment or extra length needed for anchoring, trimming, and leveling. Use zero if your design uses a surface-mounted detail and no extra post length is required.
4) How is waste applied?
Waste is applied as a multiplier to linear feet and board feet after the base calculation. It helps cover cuts, defects, end trimming, and jobsite handling losses.
5) Are stock piece counts exact?
They are planning estimates. Actual purchasing can change with supplier lengths, splice locations, grain selection, defects, and your cut optimization strategy.
6) What unit does cost use?
Cost uses your entered price per board foot. If your supplier prices by piece instead, use the board-foot output as a planning guide and compare it against local stock pricing.
7) Can I use this for attached pergolas?
Yes, but only as a rough lumber takeoff. Attached designs may use fewer posts, different beams, or a ledger, so adjust the framing logic to match your structure.
8) Is this a structural design tool?
No. It is a quantity and budgeting calculator. Final structural sizes, spans, footings, and connections should follow local code requirements and a qualified design review.