Steel pedestrian gate: cutting-list calculator
Give the width and height of the leaf and you get the cutting list for the frame, the ribs and the brace, the mass of steel and sheet, the length of welds and the current.
A worked example: a 1000 × 1800 leaf
The commonest size: about a metre of opening, an 1800 mm leaf, a frame of 40×20×2, two vertical ribs, a brace and two posts set 700 mm into the ground.
| Item | Section | Length, mm | Qty |
|---|---|---|---|
| Leaf frame, stiles | 40x20x2 | 1800 | 2 |
| Leaf frame, rails | 40x20x2 | 920 | 2 |
| Vertical rib | 40x20x2 | 1720 | 2 |
| Diagonal brace | 40x20x2 | 1951 | 1 |
| Post | 40x20x2 | 2500 | 2 |
Mass is worked out without the corner radii of the section, so it comes out two to three per cent below the standard tables. No allowance is added for saw kerf or cutting errors: when buying, add one commercial length.
The brace matters more than the wall thickness
A rectangle of four tubes is a mechanism, not a structure: four hinges and no bracing at all. However well it is welded, it folds into a parallelogram over time, and the gate starts catching the ground with the corner on the lock side.
The cure is not thickness but geometry. A brace splits the rectangle into two triangles, and a triangle does not change shape. The direction matters:
- Right: from the bottom corner on the hinge side to the top corner on the lock side. It works in compression and the weight of the leaf travels down it into the post.
- Worse: the other way round. Then it works in tension through the welds, and any weak weld turns into sag.
Posts
Wind pushes on solid sheet harder than people expect: a 1 × 1.8 m leaf is almost two square metres of sail. The post is therefore chosen for overturning moment, not for the weight of the gate.
- Section from 60×60×3 for leaves up to 1.2 m, and 80×80×3 for anything wider or from 2 m tall.
- Embedment below the frost line, usually 0.8–1.2 m.
- Gravel in the bottom of the hole, 100–150 mm, so water drains instead of freezing under the end.
- Cap the top of the post. An open tube collects water and splits along the seam in the first hard frost.
Welding settings
A 2 mm wall is thin material and the corner of the frame burns through in a second. The values are the same as on the welding square tube page; the calculator above shows the row for the wall thickness you chose.
| Wall, mm | Section | MIG/MAG | MMA |
|---|---|---|---|
| 1.2 | 20×20, 20×40 | 0.8 mm · 50–70 A · 16–17 V | 2.0 mm · 50–65 A, stitch welding |
| 1.5 | 40×20, 40×40 | 0.8 mm · 70–90 A · 17–18 V | 2.0 mm · 55–70 A, stitch welding |
| 2.0 | 40×40, 60×40 | 0.8 mm · 90–110 A · 17–19 V | 2.5 mm · 70–90 A |
| 3.0 | 60×40, 80×40 | 0.8–1.0 mm · 120–140 A · 19–21 V | 3.2 mm · 90–120 A |
| 4.0 | 80×40, 100×50 | 1.0 mm · 140–170 A · 19–21 V | 3.2 mm · 110–140 A |
What usually spoils the job
| What went wrong | Cause | How to avoid it |
|---|---|---|
| The frame twisted | Welds run one after another on the same side | Alternate corners, weld in short runs |
| The diagonals came out unequal | Nobody checked them before tacking | Measure both diagonals twice |
| Burnt through the wall | Too much current for 1.2–1.5 mm | Turn it down, stitch it with pauses |
| The corner welded on one side only | Saving time | Weld both sides wherever the joint takes load from two directions |
| Rust from the inside within a year | Open ends | Caps, or weld them shut |
Frequently asked questions
What section for a gate?
The leaf frame, 40×20×2 or 40×40×2: the first lighter and cheaper, the second stiffer and more forgiving of rough fit-up. Posts from 60×60×3; over two metres tall or with solid sheet, 80×80×3.
What is the brace for and which way does it go?
A rectangle of four tubes folds into a parallelogram under its own weight. The brace splits it into two triangles. It runs from the bottom corner on the hinge side to the top corner on the lock side: that way it works in compression and the leaf stops sagging.
How much does a finished gate weigh?
A 1000×1800 leaf in 40×20×2 with 0.5 mm profiled sheet is about 28 kg including the covering. That matters for hinges: two rated at 100 kg have plenty in hand, but with solid sheet and wind three are usual.
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