The charts below are dimensional data that I find useful to have around. There are columns for the converted scale measurements for most scales from Z to F. I also added the A (for Almost) scale of 1:29.Where a wire gauge or size is given, it is the closest match for the decimal dimension given.
Additional information available on the net: Nelson Kennedy's HO scale specific info
See the main data page for other sites with technical information, mostly related to full size railroad equipment and practices. It is down at the bottom of the web page.
Jump to: Steam Locomotive Piping
Jump to: Tender Piping
Jump to: Freight Car Brake Piping
| Useful Standard Dimensions, American Practice | |||||||||||
| Scale | Prototype | Z | N | HO | S | O | #1 | A | G | F | |
| Ratio, 1: | 1 | 220 | 160 | 87.1 | 64 | 48 | 32 | 29 | 22.5 | 20.3 | |
| Track Centers* | - | 1" | 1" | 2" | 2.75" | 4" | 6" | 6" | 8.5" | 9.5" | |
| old mainline | 11 ft | 0.6000 | 0.8250 | 1.5155 | 2.0625 | 2.7500 | 4.1250 | 4.5517 | 5.8667 | 6.5025 | |
| mainline | 15 ft | 0.8182 | 1.1250 | 2.0666 | 2.8125 | 3.7500 | 5.6250 | 6.2069 | 8.0000 | 8.8670 | |
| straight track yards, min. | 13 ft | 0.7091 | 0.9750 | 1.7910 | 2.4375 | 3.2500 | 4.8750 | 5.3793 | 6.9333 | 7.6847 | |
| yard tracks | 20 ft | 1.0909 | 1.5000 | 2.7555 | 3.7500 | 5.0000 | 7.5000 | 8.2759 | 10.6667 | 11.8227 | |
| Track centers, double track on curves | - | 1" | 1.5" | 3" | 4.125" | 6" | 9" | 9" | 10" | 10" | |
| Industry tracks, city: Track Radius | - | 5.75" | 7.75" | 12" | 16" | 21.75" | 32.75" | 36" | 46.5" | 51.5" | |
| Industry tracks, road: Track Radius | - | 7" | 9.75" | 18" | 27" | 36" | 54" | 59.5" | 77" | 85" | |
| Passing, diesel loco, branch line: Track Radius |
- | 7" | 9.75" | 18" | 27" | 36" | 54" | 59.5" | 77" | 85" | |
| Mainline freight only: Track Radius | - | 8.625" | 11.84" | 21.75" | 29.6" | 39.5" | 59.25" | 65.325" | 84" | 93.325" | |
| Std mainline, passenger, steam loco: Track Radius |
- | 8.75" | 12" | 24" | 36" | 48" | 72" | 79.5" | 102.5" | 113.5" | |
| Broad track radius | - | 11" | 15" | 30" | 45" | 60" | 90" | 99.25" | 128" | 141.875" | |
| Freight Yard (appearance only) Track Radius |
- | 13" | 18" | 36" | 54" | 72" | 108" | 119" | 170.25" | 188.75" | |
| Freight Yard Switching leads | - | 8.75" | 12" | 24" | 36" | 48" | 72" | 79.5" | 102.5" | 113.5" | |
| Average tie, height | 7" | 0.0318 | 0.0438 | 0.0804 | 0.1094 | 0.1458 | 0.2188 | 0.2414 | 0.3111 | 0.3448 | |
| Average tie, width | 9" | 0.0409 | 0.0563 | 0.1033 | 0.1406 | 0.1875 | 0.2813 | 0.3103 | 0.4000 | 0.4433 | |
| Average tie, length | 8.5 ft | 0.4636 | 0.6375 | 1.1711 | 1.5938 | 2.1250 | 3.1875 | 3.5172 | 4.5333 | 5.0246 | |
| Average ballast width at base | 16 ft | 0.8727 | 1.2000 | 2.2044 | 3.0000 | 4.0000 | 6.0000 | 6.6207 | 8.5333 | 9.4581 | |
| Overhead clearance | 22 ft | 1.2000 | 1.6500 | 3.0310 | 4.1250 | 5.5000 | 8.2500 | 9.1034 | 11.7333 | 13.0049 | |
| Typical min. rail to rail vertical clearance** | - | 1.75" | 2.1875" | 4" | 5.375" | 7" | 10.5" | 14" | 14.5" | 15" | |
| Min clearance, track center to structure trackside | 8 ft | 0.4364 | 0.6000 | 1.1022 | 1.5000 | 2.0000 | 3.0000 | 3.3103 | 4.2667 | 4.7291 | |
| Average car width | 10 ft | 0.5455 | 0.7500 | 1.3777 | 1.8750 | 2.5000 | 3.7500 | 4.1379 | 5.3333 | 5.9113 | |
| Coupler height | 34.5" | 0.1568 | 0.2156 | 0.3961 | 0.5391 | 0.7188 | 1.0781 | 1.1897 | 1.5333 | 1.6995 | |
| Common freight car wheel diameter | 33" | 0.1500 | 0.2063 | 0.3789 | 0.5156 | 0.6875 | 1.0313 | 1.1379 | 1.4667 | 1.6256 | |
| Common passenger car wheel diameter | 36" | 0.1636 | 0.2250 | 0.4133 | 0.5625 | 0.7500 | 1.1250 | 1.2414 | 1.6000 | 1.7734 | |
| Common diesel wheel diameter | 40" | 0.1818 | 0.2500 | 0.4592 | 0.6250 | 0.8333 | 1.2500 | 1.3793 | 1.7778 | 1.9704 | |
| Common freight car wheel diam., narrow gauge | 26" | 0.1182 | 0.1625 | 0.2985 | 0.4063 | 0.5417 | 0.8125 | 0.8966 | 1.1556 | 1.2808 | |
| * Figures based on NMRA straight track practices. | |||||||||||
| ** Arbitrary. Figure depth of rail, ties, ballast, roadbed and bridge structure underhang, and add to min. clearance to get actual separation needed, rail to rail. | |||||||||||
| Scale | Prototype | Z | N | HO | S | O | #1 | A | G | F | |
| Ratio, 1: | 1 | 220 | 160 | 87.1 | 64 | 48 | 32 | 29 | 22.5 | 20.3 | |
| Typical freightcar grabiron diameter | 0.75" | 0.0034 | 0.0047 | 0.0086 | 0.0117 | 0.0156 | 0.0234 | 0.0259 | 0.0333 | 0.0369 | |
| wire gauge | 37 | 37 | 31 | 29 | 26 | 23 | 23 | 20 | 19 | ||
| wire size | 1/64" | 3/128" | 3/128" | 1/16" | |||||||
| finger clearance | 2.5" | 0.0114 | 0.0156 | 0.0287 | 0.0391 | 0.0521 | 0.0781 | 0.0862 | 0.1111 | 0.1232 | |
| Grabirons, locomotives | 0.875" | 0.0040 | 0.0055 | 0.0100 | 0.0137 | 0.0182 | 0.0273 | 0.0302 | 0.0389 | 0.0431 | |
| wire gauge | 36 | 36 | 30 | 27 | 25 | 21 | 21 | 18 | 17 | ||
| Grabirons, locomotives, switchers - pilot: front, rear | 1" | 0.0045 | 0.0063 | 0.0115 | 0.0156 | 0.0208 | 0.0313 | 0.0345 | 0.0444 | 0.0493 | |
| wire gauge | 34 | 34 | 29 | 26 | 24 | 20 | 20 | 17 | 16 | ||
| wire size | 1/64" | 1/32" | 1/32" | 3/64" | |||||||
| Grabirons, locomotives, switchers - pilot: clearance | 4" | 0.0182 | 0.0250 | 0.0459 | 0.0625 | 0.0833 | 0.1250 | 0.1379 | 0.1778 | 0.1970 | |
| Uncoupling levers, clearance | 2" | 0.0091 | 0.0125 | 0.0230 | 0.0313 | 0.0417 | 0.0625 | 0.0690 | 0.0889 | 0.0985 | |
| Tender, handrail clearance, min | 24" | 0.1091 | 0.1500 | 0.2755 | 0.3750 | 0.5000 | 0.7500 | 0.8276 | 1.0667 | 1.1823 | |
| Tender, handrail clearance, max | 30" | 0.1364 | 0.1875 | 0.3444 | 0.4688 | 0.6250 | 0.9375 | 1.0345 | 1.3333 | 1.4778 | |
| Handrail, locomotive boiler | 1.375" | 0.0063 | 0.0086 | 0.0158 | 0.0215 | 0.0286 | 0.0430 | 0.0474 | 0.0611 | 0.0677 | |
| wire gauge | 31 | 31 | 26 | 23 | 21 | 17 | 17 | 14 | 13 | ||
| wire size | 1/64" | 1/16" | |||||||||
| Running board, minimum width | 10" | 0.0455 | 0.0625 | 0.1148 | 0.1563 | 0.2083 | 0.3125 | 0.3448 | 0.4444 | 0.4926 | |
| Running board, wood, minimum thickness | 1.5" | 0.0068 | 0.0094 | 0.0172 | 0.0234 | 0.0313 | 0.0469 | 0.0517 | 0.0667 | 0.0739 | |
| Brake Staff diameter | 1.25" | 0.0057 | 0.0078 | 0.0144 | 0.0195 | 0.0260 | 0.0391 | 0.0431 | 0.0556 | 0.0616 | |
| wire gauge | 35 | 32 | 27 | 24 | 22 | 18 | 17 | 15 | 14 | ||
| wire size | 1/16" | ||||||||||
| Steam Locomotive Piping, Sch 40 steel | |||||||||||
| Scale | Prototype | Z | N | HO | S | O | #1 | A | G | F | |
| Ratio, 1: | 1 | 220 | 160 | 87.1 | 64 | 48 | 32 | 29 | 22.5 | 20.3 | |
| Water Feed Pipe, small | 3" nom (3.5") | 0.0159 | 0.0219 | 0.0402 | 0.0547 | 0.0729 | 0.1094 | 0.1207 | 0.1556 | 0.1724 | |
| wire gauge | 23 | 23 | 18 | 15 | 13 | 9 | 9 | 6 | 5 | ||
| wire size | 7/128" | 7/64" | 7/64" | 5/32" | 11/64" | ||||||
| Water Feed Pipe, large | 3 1/2"nom (4") | 0.0182 | 0.0250 | 0.0459 | 0.0625 | 0.0833 | 0.1250 | 0.1379 | 0.1778 | 0.1970 | |
| wire gauge | 22 | 22 | 16 | 14 | 12 | 8 | 8 | 5 | 4 | ||
| wire size | 1/16" | 1/8" | 1/8" | 3/16" | |||||||
| Water Feed Pipe, max | 4"nom (4.5") | 0.0205 | 0.0281 | 0.0517 | 0.0703 | 0.0938 | 0.1406 | 0.1552 | 0.2000 | 0.2217 | |
| wire gauge | 21 | 21 | 16 | 13 | 13 | 7 | 7 | 4 | 3 | ||
| wire size | 9/128" | 3/32" | 9/64" | 9/64" | 7/32" | ||||||
| Steam Pipe to Compressor, min | 1 1/4"nom (1.66") | 0.0075 | 0.0104 | 0.0191 | 0.0259 | 0.0346 | 0.0519 | 0.0572 | 0.0738 | 0.0818 | |
| wire gauge | 30 | 30 | 24 | 22 | 19 | 16 | 16 | 13 | 12 | ||
| Steam Pipe to Compressor, max | 1 1/2"nom (1.9") | 0.0086 | 0.0119 | 0.0218 | 0.0297 | 0.0396 | 0.0594 | 0.0655 | 0.0844 | 0.0936 | |
| wire gauge | 28 | 28 | 23 | 21 | 18 | 15 | 15 | 12 | 11 | ||
| wire size | 5/128" | 11/128" | |||||||||
| Steam Pipe to generator, overflow pipe | 1 1/2"nom (1.9") | 0.0086 | 0.0119 | 0.0218 | 0.0297 | 0.0396 | 0.0594 | 0.0655 | 0.0844 | 0.0936 | |
| wire gauge | 28 | 28 | 23 | 21 | 18 | 15 | 15 | 12 | 11 | ||
| wire size | 5/128" | 11/128" | |||||||||
| Steam pipe, exhaust to smokebox, small | 1"nom (1.315") | 0.0060 | 0.0082 | 0.0151 | 0.0205 | 0.0274 | 0.0411 | 0.0453 | 0.0584 | 0.0648 | |
| wire gauge | 31 | 31 | 26 | 24 | 21 | 18 | 18 | 15 | 14 | ||
| wire size | 1/64" | ||||||||||
| Steam pipe, exhaust to smokebox, large | 2"nom (2.375") | 0.0108 | 0.0148 | 0.0273 | 0.0371 | 0.0495 | 0.0742 | 0.0819 | 0.1056 | 0.1170 | |
| wire gauge | 27 | 27 | 21 | 19 | 16 | 13 | 13 | 10 | 9 | ||
| Sand pipes | 2"nom (2.375") | 0.0108 | 0.0148 | 0.0273 | 0.0371 | 0.0495 | 0.0742 | 0.0819 | 0.1056 | 0.1170 | |
| wire gauge | 27 | 27 | 21 | 19 | 16 | 13 | 13 | 10 | 9 | ||
| Brake pipe | 1 1/4"nom (1.66") | 0.0075 | 0.0104 | 0.0191 | 0.0259 | 0.0346 | 0.0519 | 0.0572 | 0.0738 | 0.0818 | |
| wire gauge | 30 | 30 | 24 | 22 | 19 | 16 | 16 | 13 | 12 | ||
| Air Signal Line | 1"nom (1.315") | 0.0060 | 0.0082 | 0.0151 | 0.0205 | 0.0274 | 0.0411 | 0.0453 | 0.0584 | 0.0648 | |
| wire gauge | 31 | 31 | 26 | 24 | 21 | 18 | 18 | 15 | 14 | ||
| wire size | 1/64" | ||||||||||
| Train Line (engine brakes) |
2"nom (2.375") | 0.0108 | 0.0148 | 0.0273 | 0.0371 | 0.0495 | 0.0742 | 0.0819 | 0.1056 | 0.1170 | |
| wire gauge | 27 | 27 | 21 | 19 | 16 | 13 | 13 | 10 | 9 | ||
| Steam pipe (passenger only, heat) | 2 1/2"nom (2.875") | 0.0131 | 0.0180 | 0.0330 | 0.0449 | 0.0599 | 0.0898 | 0.0991 | 0.1278 | 0.1416 | |
| wire gauge | 25 | 25 | 20 | 17 | 15 | 11 | 11 | 8 | 7 | ||
| Tender Piping, Sch 40 steel | |||||||||||
| Scale | Prototype | Z | N | HO | S | O | #1 | A | G | F | |
| Ratio, 1: | 1 | 220 | 160 | 87.1 | 64 | 48 | 32 | 29 | 22.5 | 20.3 | |
| Brake cylinder pipe | 1"nom (1.315") | 0.0060 | 0.0082 | 0.0151 | 0.0205 | 0.0274 | 0.0411 | 0.0453 | 0.0584 | 0.0648 | |
| wire gauge | 31 | 31 | 26 | 24 | 21 | 18 | 18 | 15 | 14 | ||
| wire size | 1/64" | ||||||||||
| Brake pipe | 1 1/2"nom (1.9") | 0.0086 | 0.0119 | 0.0218 | 0.0297 | 0.0396 | 0.0594 | 0.0655 | 0.0844 | 0.0936 | |
| wire gauge | 28 | 28 | 23 | 21 | 18 | 17 | 15 | 12 | 11 | ||
| wire size | 5/128" | 11/128" | |||||||||
| Signal pipe | 1"nom (1.315") | 0.0060 | 0.0082 | 0.0151 | 0.0205 | 0.0274 | 0.0411 | 0.0453 | 0.0584 | 0.0648 | |
| wire gauge | 31 | 31 | 26 | 24 | 21 | 18 | 18 | 15 | 14 | ||
| wire size | 1/64" | ||||||||||
| Steam pipe (passenger only, heat) | 2 1/2"nom (2.875") | 0.0131 | 0.0180 | 0.0330 | 0.0449 | 0.0599 | 0.0898 | 0.0991 | 0.1278 | 0.1416 | |
| wire gauge | 25 | 25 | 20 | 17 | 15 | 11 | 11 | 8 | 7 | ||
| Water hose (1/2" to 1" larger than water feed) |
4" | 0.0182 | 0.0250 | 0.0459 | 0.0625 | 0.0833 | 0.1250 | 0.1379 | 0.1778 | 0.1970 | |
| wire gauge | 22 | 22 | 16 | 14 | 12 | 8 | 8 | 5 | 4 | ||
| wire size | 1/16" | 1/8" | 1/8" | 3/16" | |||||||
| Water hose (1/2" to 1" larger than water feed) |
5 1/2" | 0.0250 | 0.0344 | 0.0631 | 0.0859 | 0.1146 | 0.1719 | 0.1897 | 0.2444 | 0.2709 | |
| wire gauge | 19 | 19 | 14 | 12 | 9 | 5 | 5 | 3 | 2 | ||
| wire size | 1/16" | 11/128" | 11/64" | 11/64" | |||||||
| Freight Car brake piping, Sch 40 steel | |||||||||||
| Scale | Prototype | Z | N | HO | S | O | #1 | A | G | F | |
| Ratio, 1: | 1 | 220 | 160 | 87.1 | 64 | 48 | 32 | 29 | 22.5 | 20.3 | |
| Train Line (brake line) |
1 1/4"nom (1.666) | 0.0076 | 0.0104 | 0.0191 | 0.0260 | 0.0347 | 0.0521 | 0.0574 | 0.0740 | 0.0821 | |
| wire gauge | 30 | 30 | 24 | 22 | 19 | 16 | 16 | 13 | 12 | ||
| wire size | 1/16" | 11/128" | 11/64" | 11/64" | |||||||
| Branch pipe to triple valve (ABD) | 1"nom (1.315") | 0.0060 | 0.0082 | 0.0151 | 0.0205 | 0.0274 | 0.0411 | 0.0453 | 0.0584 | 0.0648 | |
| wire gauge | 31 | 31 | 26 | 24 | 21 | 18 | 18 | 15 | 14 | ||
| wire size | 1/64" | ||||||||||
| Lines to air reservoir | 3/4"nom (1.050") | 0.0048 | 0.0066 | 0.0121 | 0.0164 | 0.0219 | 0.0328 | 0.0362 | 0.0467 | 0.0517 | |
| wire gauge | 37 | 34 | 28 | 26 | 23 | 20 | 19 | 17 | 16 | ||
| wire size | 1/64" | ||||||||||
| Line to brake cylinder | 3/4"nom (1.050") | 0.0048 | 0.0066 | 0.0121 | 0.0164 | 0.0219 | 0.0328 | 0.0362 | 0.0467 | 0.0517 | |
| wire gauge | 37 | 34 | 28 | 26 | 23 | 20 | 19 | 17 | 16 | ||
| wire size | 1/64" | ||||||||||
| Line to retaining valve | 3/8"nom (.675) | 0.0031 | 0.0042 | 0.0077 | 0.0105 | 0.0141 | 0.0211 | 0.0233 | 0.0300 | 0.0333 | |
| wire gauge | 40 | 37 | 32 | 30 | 27 | 24 | 23 | 20 | 19 | ||
If you have comments, suggestions on what you would like to see
or data you might like, you can email me at:
Rick Blanchard - rick@urbaneagle.com
--Back to da data.--
