An envelope, printed where the window is ENVELOPE

Every failed attempt costs an envelope

Printing an envelope ought to be the easiest thing a computer does and is one of the most annoying, for three reasons that compound. The page size is not one the software expects, so the driver improvises. The address has to land inside a window whose position is a property of the envelope rather than of the printer, so nothing in the print dialogue knows where it is. And you cannot test it: every attempt uses a real envelope, and you find out it was wrong after it has been used.

So this does the boring parts properly. The standard sizes are here in millimetres (DL, C5, C4, C6, and the American numbers) because “DL” means an exact rectangle and a tool that made you look it up would be missing half the job. The address block is positioned in millimetres from the top left, with the usual window positions as starting points, so you are adjusting from something close rather than guessing from nothing.

The test print is the whole tool

There is a mode that draws the window outline on the screen, so you can see whether the address sits inside it before feeding anything in. That is useful. The mode that matters is the one that prints that outline on ordinary A4.

One sheet of paper, held up to the light against the actual envelope, answers the question no amount of measuring on screen can: is the address inside the window, on this envelope, from this printer, at this printer's idea of scale. It costs a sheet of paper instead of an envelope, and you can do it as many times as you like.

Do it at least once for each box of envelopes. Window position is not standardised as tightly as the outside dimensions, and two boxes marked DL from two suppliers can put the window in noticeably different places.

Getting the printer to stop helping

Most envelopes that come out wrong come out wrong for one reason: the print dialogue scaled the page. Look for “Fit to page”, “Shrink to printable area” or a scale percentage, and set it to 100% or Actual size. If the scale is not 100% the measurements on this page are irrelevant, because everything shifts by the same proportion and the error is invisible: it looks like a neat print that is in the wrong place.

Then set the paper size to the envelope, not to A4 with an envelope in the tray. Check which edge your printer feeds first and which way up it expects the envelope; there is usually a diagram on the tray, and it is usually the thing that was wrong. Feed one envelope at a time.

If the address lands consistently a few millimetres out in the same direction, do not fight the printer; move the address block by that many millimetres here and print again. The number that works for your printer will keep working.

Alongside: LABELS prints a sheet of labels measured the same way, MERGE makes one letter per row from a template and a list, PAPER prints graph and ruled paper at a size you can prove, and Contacts holds the addresses. Nothing you type is uploaded.