Pergola Material Calculator
Posts, beams, rafters and slats for a pergola build.
Enter your values
Enter the pergola length in ft.
Enter the pergola width in ft.
Enter the rafter spacing in in.
Enter the purlin spacing in in.
Enter the cost per linear foot in $.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Posts
- 4 x 10 ft (6x6 recommended)
- Beams
- 4 x 12 ft
- Rafters
- 10 x 10 ft
- Purlins
- 11 x 12 ft
- Total lumber
- 320 linear ft
- Lumber cost
- $1,120.00
Working
- 1rafters 10 + purlins 11 -> 320 linear ft total
Quick answer
A pergola needs 4+ posts, two beams per side, rafters at your chosen spacing across the span, and optional top purlins.
rafters = width / spacing + 1
At a glance
| What it does | Posts, beams, rafters and slats for a pergola build. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Pergola length, Pergola width, Rafter spacing, Purlin spacing, Cost per linear foot |
| Main output | Posts |
| Formula | rafters = width / spacing + 1 |
| Cost | Free — no sign-up, no download |
How to use the Pergola Material Calculator
- 1Set the pergola footprint and choose rafter spacing - 16 to 24 inches is typical.
- 2Add purlins on top if you want more shade.
- 3Price the total linear feet at your local lumber rate.
Inputs explained
- Pergola length(ft)
- Enter the pergola length in ft.
- Pergola width(ft)
- Enter the pergola width in ft.
- Rafter spacing(in)
- Enter the rafter spacing in in.
- Purlin spacing(in)
- Enter the purlin spacing in in.
- Cost per linear foot($)
- Enter the cost per linear foot in $.
Worked example
Using the values the calculator loads with:
Inputs
- Pergola length12 ft
- Pergola width10 ft
- Rafter spacing16 in
- Purlin spacing12 in
- Cost per linear foot3.50 $
Results
- Posts4 x 10 ft (6x6 recommended)
- Beams4 x 12 ft
- Rafters10 x 10 ft
- Purlins11 x 12 ft
- Total lumber320 linear ft
- Lumber cost$1,120.00
- rafters 10 + purlins 11 -> 320 linear ft total
Frequently asked questions
How much shade does a pergola give?
Rafters alone give roughly 30 to 40% shade. Adding purlins on top pushes it toward 60 to 70% at midday.
What size posts for a pergola?
6x6 for anything over 8 ft tall or 10 ft span. 4x4 posts look spindly and flex in wind.
What do I need to enter into the Pergola Material Calculator?
Just 5 values: pergola length, pergola width, rafter spacing, purlin spacing, cost per linear foot. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Pergola Material Calculator work out the answer?
A pergola needs 4+ posts, two beams per side, rafters at your chosen spacing across the span, and optional top purlins. It applies the formula rafters = width / spacing + 1 and shows the working so you can check each step by hand.
Is the Pergola Material Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.