Isometric paper, quarter-inch
An isometric grid stepped in quarter inches rather than millimetres, for shop work where every material you are drawing is specified in inches.
Opens with these settings already loaded. Change anything you like, then download as PDF, PNG or SVG.
Isometric in inches, for shop work
Timber, plywood, fasteners and shop measurements in North America are imperial, and an isometric grid in millimetres forces a conversion at every edge you draw. At quarter-inch spacing each grid step is a quarter inch along all three axes, so a 12 inch board is 48 steps and a ¾ inch thickness is three. Counting replaces arithmetic, which is the whole reason to draw on a grid in the first place.
Sketching joinery
Isometric is unusually good at joints. A mortise and tenon, a dovetail or a half-lap is laborious to describe in plan and elevation and immediately obvious in an isometric sketch, because all three faces are visible at once and every edge still measures true. Cabinetmakers drew this way long before CAD existed, and a printed grid removes the only genuinely fiddly part of doing it by hand.
It is not how the eye sees it
On an isometric grid parallel edges stay parallel and distant edges stay the same size as near ones. That is exactly what makes the drawing measurable, and exactly what makes it look faintly wrong — a cube drawn isometrically reads as slightly splayed. If you want the drawing to look convincing rather than to be measured off, use a perspective grid and accept that you cannot scale from it.
Printing it accurately
This only measures correctly if your printer doesn't rescale the page. In the print dialog set Scale: 100% — not "Fit to page" or "Shrink oversized pages". If you're not sure it worked, print the calibration page, measure the ruler on it with a real ruler, and it will tell you exactly what your printer is doing to the page.