An online calculator for electricians. It shows where to put the marks and how many millimetres to cut away so a straight perforated tray can be bent on site — no factory bends or fittings needed. It handles turns, going round obstructions, rises and drops, and radius runs, and draws the job up with dimensions. The app installs on your phone in one tap and works with no internet — it keeps calculating on site where there is no signal.
The most common job: swinging a run through 45 or 90 degrees. A triangular wedge is cut from the base — tip on the outer edge, opening on the inner edge. The side that ends up inside the turn is cut through its full height; the outer side is left alone and bends by itself. The size comes from the tray width and the angle. For 300 mm tray at 45° that is 124 mm either side of the bend line, so 248 mm of full opening. For 200 mm at the same angle it is 83 mm each way. At 90° the cut equals the tray width.
Where something is in the way and the run has to step aside then carry on parallel, two cuts are made facing each other, on opposite sides of the tray. The key figure is not the cut itself but the distance between the notches: it allows for the metal removed by the cut. Without that allowance the pieces will not line up and the run drifts. The easiest way is to measure from the edge of the first notch to the centre of the second.
To lift or drop a run, a wedge is cut from both sides and the base between the tips simply folds. Here the size comes from the height of the side, not the tray width, so the cut is several times smaller: with a 60 mm side at 45° it is about 25 mm each way. An inside bend (a dip) folds cleanly. An outside bend (a hump) needs the bottom trimming to fit or the joint welded — there is not enough metal at the edges.
A rise or drop to a set height is two vertical angles in a row. The calculator works out the length of sloped tray between them. One angle is always an inside bend and the other an outside bend, so it pays to plan the awkward one where you can actually get at it to weld.
Tray will not hold a smooth curve: it is built up from a series of identical small notches, each swinging the run through a little angle. Enter the diameter and the number of notches and the calculator gives the marking pitch, the size of each cut, and how far the run will sit off a true circle. More notches means a smoother curve but more work.
Cut each way from the bend line, in millimetres. Full opening is double that. Figures are for a horizontal turn, where the tray width sets the size. Works for perforated, solid-bottom and ladder tray from any maker.
| Tray width | 30° | 45° | 60° | 90° |
|---|---|---|---|---|
| 100 mm | 27 | 41 | 58 | 100 |
| 150 mm | 40 | 62 | 87 | 150 |
| 200 mm | 54 | 83 | 115 | 200 |
| 300 mm | 80 | 124 | 173 | 300 |
| 400 mm | 107 | 166 | 231 | 400 |
| 500 mm | 134 | 207 | 289 | 500 |
124 mm each way from the bend line, so 248 mm of opening along the inner edge. For 200 mm tray it is 83 mm each way, for 100 mm it is 41 mm. There is a table above for common widths and angles, and the calculator will do any size.
The same way as 45, just a bigger cut: at 90 degrees it equals the tray width. On 300 mm tray that is 300 mm each way from the bend line. The wedge comes out as a right angle, with the tip still on the outer edge. Where space is tight it is often better to make two 45 degree turns instead of one at 90.
Yes — the working is the same for perforated, solid-bottom and ladder tray, since the geometry does not depend on the perforations. On perforated tray it is even easier: the holes help you line the marks up. Just keep the bend line off a row of holes, or the edge may tear at the fold. On ladder tray, keep the bend line clear of the rungs.
That is the Offset mode: enter how far the run has to step across and the calculator works out the distance between the two notches. The first takes the run sideways, the second brings it back parallel to the original. The notches go on opposite sides of the tray.
Steel tray of any kind: perforated, solid-bottom and ladder, from any manufacturer — the geometry is the same. Two neighbouring products are a different matter. Plastic trunking is cut at an angle in a mitre box, not notched. Wire mesh tray is turned by cutting through the wires with croppers, so there is nothing to work out there either.
Straight across, not on the diagonal. The lid of one run is cut square along the edge, and the lid of the run beyond the turn is pushed up to it at 90 degrees. It seems logical to mitre it at 45 like trunking, but it is not worth it: a diagonal cut is longer and easier to wander, a piece without its folded edge loses stiffness, and it looks worse. What matters is a straight cut, so mark the line with a square.
Not the way you would on steel tray: no wedge is cut out, the trunking is cut on the diagonal. A mitre box is quickest — it holds the 45 degrees for you. But there may be no mitre box on site, and then you mark it out instead. Put a mark on one side wall, then a second one on the opposite wall offset by the width of the trunking, and carry the line across the base and both walls, right round the profile. Then cut along that line with a hacksaw: having the mark on every face stops the blade wandering. Two such pieces put together make a 90 degree corner, like skirting board. The lid is marked and cut the same way. There is nothing to work out: the width of the trunking sets the size.
Usually an angle grinder with a cutting disc, or tin snips — on thin galvanised tray snips are often neater and leave no burnt edge. Clean up and treat the edge afterwards: the galvanising is broken where you cut, and it will rust if left.
Start with the bend line — a line across the base where the run will turn. Measure off it both ways and those marks give you the edges of the cut. Mark it all out on straight tray before bending: once the first fold is made the geometry shifts and the figures go out.
Yes, and there is nothing to download: tap Install in the site header and the calculator goes on your home screen like an ordinary app — no store, no sign-up, no updates to chase. Once installed it works with no internet, so it keeps calculating on site with no signal. On iPhone install it by hand: Share → Add to Home Screen.
The geometry is exact, but it does not account for metal thickness or the radius at the fold. On thin galvanised tray the difference is within a millimetre. It is worth trying the first cut of a new size on an offcut.
Electricians and installation crews running cable tray on site: when the factory bend you need is not to hand and the run has to turn or clear an obstruction today. The calculator is free, with no sign-up and no ads, and works with tray from any manufacturer.