Architect Scale · 1:20 on A3 · Portrait

About this template

Detail-scale grid for the part of a drawing set where construction actually happens. At 1:20 a 25 mm cell represents 500 mm in the world, comfortable for window heads, junction details, stair sections and sanitary fittings. Lines are calibrated so a single A3 sheet holds an entire wall section. See also: A short reading list on technical drawing standards can help you put any of these grids in their historical and standards-based context.

Best used for

• Wall-section construction details
• Stair detail drawings
• Window head, jamb and sill details
• Bathroom layouts and wet-room sections

Why A3 in portrait

Doubles the area of A4 along the long edge - the workhorse for plan drawings, schematics and concept sketches in metric studios. The portrait orientation gives you 297 mm of horizontal run and 420 mm of vertical, which suits tall subjects - elevations, sections, single-column drawings - where the eye reads top-to-bottom. Trim and bleed allowances on consumer printers will normally remove a 5 mm strip from each edge; this grid is generated to remain measurable even after that trim, with no critical content placed inside the printer-margin band.

Standards and lineage

Recommended detail scale per ISO 5455:1979. The A3 sheet itself follows ISO 216, and the title-block conventions assumed by this template come from ISO 5457:1999 - the international standard governing how technical drawings are framed, dated, and signed. Background reading: See our scale-and-projection guides for a deeper dive on how all the standards in this lineage interact in practice.

A short history of this grid

1:20 detailing standardised across British and Northern European practice in the 1960s, replacing the older 1:24 (1/2" = 1'-0") imperial detail scale.

Printing notes

For accurate output, print at 100 % scale - never "fit to page", which silently shrinks the sheet by 4–6 % and breaks every measured cell. Use a laser printer if the grid will be traced over with ink, since inkjet inks bleed through technical pen and pencil. If your printer cannot handle the full A3 sheet, scale the SVG to the next-smaller paper size before printing - every GridCraft grid is delivered as vector artwork so it scales cleanly. The downloaded SVG carries the physical sheet dimensions in millimetres, so a compliant print driver should print at 1:1 by default. Our how-to-print guide walks through the calibration test in 30 seconds.

Designer's note

Specialty grids reward the discipline of choosing the right sheet for the right drawing. A Architect Scale · 1:20 on A3 is not a one-size-fits-all sheet - it's a calibrated tool for a specific class of problem. Use it where the page suits the drawing; reach for a different sheet when it doesn't. The catalogue is large precisely so you don't have to compromise on the projection, scale or sheet size.