| Scale | Ratio | Scale factor | Viewport (xp) |
|---|---|---|---|
| 1/16″ = 1′-0″ | 1:192 | 192 | 1/192xp |
| 1/8″ = 1′-0″ | 1:96 | 96 | 1/96xp |
| 3/16″ = 1′-0″ | 1:64 | 64 | 1/64xp |
| 1/4″ = 1′-0″ | 1:48 | 48 | 1/48xp |
| 3/8″ = 1′-0″ | 1:32 | 32 | 1/32xp |
| 1/2″ = 1′-0″ | 1:24 | 24 | 1/24xp |
| 3/4″ = 1′-0″ | 1:16 | 16 | 1/16xp |
| 1″ = 1′-0″ | 1:12 | 12 | 1/12xp |
| 1-1/2″ = 1′-0″ | 1:8 | 8 | 1/8xp |
| 3″ = 1′-0″ | 1:4 | 4 | 1/4xp |
| 1″ = 20′ (engineer) | 1:240 | 240 | 1/240xp |
| 1″ = 40′ (engineer) | 1:480 | 480 | 1/480xp |
| 1:50 (metric) | 1:50 | 50 | 1/50xp |
| 1:100 (metric) | 1:100 | 100 | 1/100xp |
The scale factor for 1/4" = 1'-0" is 48. One foot equals twelve inches, and a quarter inch divides into twelve inches forty-eight times, so one unit on the drawing equals forty-eight units in reality, a ratio of 1:48. That 48 is the number you set as DIMSCALE and LTSCALE in CAD, and the viewport plots at 1/48xp.
Multiply the measured length by the scale's ratio. On a 1/4"=1'-0" (1:48) drawing, a line that measures 3 inches is 3 × 48 = 144 inches = 12'-0" in reality. This converter does it for any imperial architectural, engineering or metric scale, and reverses it to tell you how large a real dimension will draw on paper.
Reprinting multiplies every dimension on the sheet by the zoom percentage. Print a 1/4"=1'-0" drawing at 50% and each dimension halves, so it now reads as 1/8"=1'-0". To go from one scale to another, set your plotter or copier to (original ratio ÷ target ratio) × 100 percent. The Reprint tab does the math and the measured-length conversion for you.
The scale factor is the ratio between model space and paper: 48 for 1/4"=1'-0", 96 for 1/8"=1'-0". It sets DIMSCALE, LTSCALE and the multiplier for model-space text: to plot 1/8" text on a 1/4" drawing you draw it 48 × 1/8" = 6" tall in model space. In a layout viewport the same scale plots at 1/48xp.
An architect's scale is based on fractions of an inch representing one foot (1/4"=1'-0", 1/8"=1'-0") and is used for buildings. An engineer's scale uses one inch representing a round number of feet (1"=20', 1"=40') and is used for site, civil and survey work. Both are just ratios (1:48, 1:240) and this tool handles either, plus metric 1:50, 1:100 and the rest.