Architectural scale, in plain language
Scale is the silent contract between a drawing and the building it represents. Pick the right ratio and the page tells the truth at a glance; pick the wrong one and either the drawing won't fit on the sheet or the detail won't survive the reduction. The European "preferred scales" listed in ISO 5455 codify a set of ratios that have been refined over a century of practice - the scales below are the ones working studios actually use.
1:20 - Construction details
The detail scale. A 25 mm cell on the page represents 500 mm in the world, which comfortably accommodates a window head, jamb, sill, or any junction between two materials. Detail drawings at 1:20 are where construction actually happens - every framer, joiner and plasterer reads them. Use 1:20 for: junction details, stair details, wet-room sections, balustrade details, parapet caps. See 1:20 templates →
1:50 - Apartment-scale plans
The default scale for residential interior layouts and individual building units. A 20 mm cell represents 1 m, so a 5 m × 4 m room snaps neatly into a 100 × 80 mm patch on the page. Furniture is recognisable; door swings are measurable. Use 1:50 for: apartment floor plans, fit-out drawings, retail interiors, hospitality layouts, bathroom plans. See 1:50 templates →
1:100 - Whole-building plans
The dominant European architectural plan scale. Every 10 mm cell is 1 m, so most domestic-scale buildings - houses, small offices, schools - fit cleanly onto an A3 or A2 sheet at this ratio. The standard scale for planning-application drawings and tender drawings across continental Europe and the United Kingdom. Use 1:100 for: whole-building floor plans, planning applications, tender drawings, fire-strategy plans. See 1:100 templates →
1:200 - Block and site plans
The intermediate scale between building and master plan. A 5 mm cell is 1 m; a small block of buildings fits onto a single A3. Useful for showing a building in its immediate site context - driveway, landscape, neighbouring structures, service runs. Use 1:200 for: site plans, landscape layouts, master-plan studies for a single plot, transport-interchange site studies. See 1:200 templates →
1:500 - Master plans
The civic scale. A 10 mm cell represents a 5 m × 5 m patch of ground. Big enough to put a city block on a single sheet without losing the ability to measure street widths, building footprints and setback distances. The default for urban-design studies, civic-scale landscape design, and brownfield redevelopment master plans. Use 1:500 for: master plans, urban-design studies, station-area planning, conservation-area appraisals. See 1:500 templates →
1:1000 and beyond - strategic plans
For neighbourhood and city-wide strategic work, ratios of 1:1000, 1:2500 and 1:5000 are used. 1:1000 templates are in the catalogue; for ratios beyond that, ordnance-survey base mapping is the better source. Buyer's guide: Comparing the major architectural scale rulers covers the physical rules to use over each scale.
Imperial counterparts
North American practice continues to use a parallel set of imperial scales. Approximate metric equivalents:
- 1/4" = 1'-0" ≈ 1:48 - residential floor plans (close cousin of 1:50)
- 1/8" = 1'-0" ≈ 1:96 - whole buildings (close cousin of 1:100)
- 1" = 20' ≈ 1:240 - block plans
- 1" = 40' ≈ 1:480 - site plans (close cousin of 1:500)
- 3" = 1'-0" ≈ 1:4 - full-size detail
The metric and imperial systems are close enough at most scales that drawings drift between them readily; for permit work in the United States stick to the imperial conventions, but for international collaboration prefer the ISO ratios.
Choosing the right scale for the right job
The classic studio rule: pick the scale that lets the smallest meaningful element on the drawing be legible at arm's length. A door swing must read as a door swing; a stair tread as a tread; a window mullion as a mullion. If the smallest element disappears at the chosen scale, step up to a larger one (smaller ratio number); if the drawing falls off the edge of the sheet, step down.
Never compromise scale to fit the sheet. Compromise the sheet - issue the drawing across multiple sheets, or print on the next size up.