How the ruler is worked out
At 1:N, one scale foot is 304.8 ÷ N mm and one scale metre is 1000 ÷ N mm. In HO (1:87.1) a scale foot is 3.499 mm, so a 40 ft boxcar is 40 × 3.499 = 140 mm long. The ruler marks every scale foot or metre with finer marks between, as fine as still prints clearly. Open this example.
The ratios used
Scale names don't always mean one ratio. These are the presets, and you can change the number in any of them.
| Scale | Ratio | Also seen |
|---|---|---|
| HO | 1:87.1 (NMRA) | 1:87 (NEM H0); 3.5 mm to the foot is 1:87.09 |
| N | 1:160 | 1:148 British N, 1:150 Japanese N |
| OO | 1:76.2 (4 mm to the foot) | 1:76 (NEM) |
| O | 1:48 US | UK 7 mm to the foot, 1:43.54 (NEM rounds it to 1:43.5); 1:45 NEM |
| S | 1:64 | |
| TT | 1:120 | |
| Z | 1:220 | |
| G and large scale | 1:22.5 (NEM II) | 1:24, 1:29, 1:32 (gauge 1), 1:20.3 (F) |
| Dollhouse | 1:12 (1 inch to the foot) | 1:24 half, 1:48 quarter, 1:144 |
Questions
Is HO scale 1:87 or 1:87.1?
Both are in use. The NMRA gives HO as 1:87.1, from 3.5 mm to the foot (exactly 1:87.09). The European NEM standard gives H0 as 1:87. Over a 20 cm ruler the difference is about 0.2 mm, so either works for scratch building.
What scale is O gauge?
It depends on where it was made. US O is 1:48 (1/4 inch to the foot). UK O is 7 mm to the foot, given as 1:43.5. The European NEM standard uses 1:45. All three run on track about 32 mm apart, so check the box or catalog before you print.
What is the difference between OO and HO?
OO models are 4 mm to the foot (1:76.2) and HO models 3.5 mm to the foot (1:87.1), so an OO figure or building is about 14% bigger than its HO version.
What scale is G scale?
G names the 45 mm track more than one scale. The NMRA lists 1:32, 1:29, 1:24, 1:22.5 and 1:20.3 trains on it, and NEM gives 1:22.5 for gauge II and 1:32 for gauge I. Check the box or catalog for yours.
Is N scale 1:160 or 1:148?
US and European N is 1:160. British N models are made at 1:148, so a British N figure is about 8% bigger. Pick N or N (British).
Can I make a 4 mm or 7 mm scale ruler?
Yes. Type the length of one scale foot in the 1: box, such as 4 mm, 7 mm or 1/4 in, and the ruler uses that exactly: 7 mm becomes 1:43.54.
How do I know the printout is the right size?
Measure the check bar at the top of the sheet with a real ruler: 0 to 10 cm must be 100 mm and 0 to 4 in must be 4 inches. If not, set Scale to 100% or Actual size in the print window (not Fit to page) and print again. From a phone, save a PDF and print that at 100%.
Sources: NMRA Standard S-3.2 Track, Standard Scale (2026) and earlier S-1.2 scale table; MOROP NEM 010, scales and gauges (2011).