Metalwork · Pergolas
Steel and aluminium pergola calculator
A free-standing 4 × 3 m pergola, 2.4 m high, with 100 × 100 × 3 posts, 120 × 60 × 3 beams and 80 × 40 × 2 rafters at 500 mm at most takes 4 posts, 2 beams and 9 rafters at 495 mm: 44.6 m of steel weighing about 251.6 kg. Change the sizes and the profiles: the calculator draws the plan and the front view and opens the cut list in the bar optimizer. It is a take-off, not a structural design: it works out no snow or wind load.
Cut list
| Profile | Piece | Length (mm) | Qty |
|---|
Loads and codes
This page counts the steel; it does not design it. Whether a 120 × 60 beam carries a 4 m span depends on the snow, the wind and the roof the pergola will take where you build, and on how the posts are anchored: that is worked out by an engineer with the loads of the code in your country. A louvred or glazed roof weighs much more than open rafters. Check the code in your country, and the planning rules of your town for a pergola against a wall or on a terrace.
How it is worked out
For the pergola above: (4000 − 100) / 4000 gives 1 bay, 2 posts per row and 4 posts of 2400 mm in two rows. Rafters 40 mm wide at 500 mm at most: ⌈(4000 − 40) / 500⌉ + 1 = 9, at (4000 − 40) / 8 = 495 mm. The 100 × 100 × 3 tube is 10000 − 94² = 1164 mm², 1164 × 7850 / 10⁶ = 9.137 kg/m; the 120 × 60 × 3 tube is 7200 − 114 × 54 = 1044 mm², 8.195 kg/m; the 80 × 40 × 2 tube is 3200 − 76 × 36 = 464 mm², 3.642 kg/m. Weight: 9.6 m × 9.137 + 8.0 m × 8.195 + 27.0 m × 3.642 = 251.6 kg. In aluminium (2700 kg/m³) the same tubes weigh 86.5 kg. The sections are sharp-cornered, as in the metal weight calculator: a rolled tube with round corners weighs a few per cent less.
What this page does not do
- It does not work out loads. No snow, wind or roof load and no check of the posts, the beams or the rafters: it is a take-off, not a structural design.
- It does not count base plates, anchors, brackets, screws, welding, the roof covering or paint.
- It is a rectangle with level beams. A sloping roof, overhangs and cantilevers are not drawn.
Questions people ask
- How many rafters does a pergola need?
- Divide the length minus one rafter width by the largest spacing, round up and add one: a 4 m pergola with 40 mm rafters at 500 mm at most takes ⌈3960 / 500⌉ + 1 = 9, at 495 mm between axes.
- How much does a steel pergola weigh?
- The 4 × 3 m pergola above, with 100 × 100 × 3 posts, 120 × 60 × 3 beams and 80 × 40 × 2 rafters, weighs about 251.6 kg in steel and 86.5 kg in aluminium.
- Does this calculator size the beams for snow and wind?
- No. It counts the pieces and their weight for the profiles you choose; whether they carry the snow, the wind and the roof is worked out by an engineer with the code in your country.