Minimum curve radius: HO and N sectional track
Each maker sells its curved sectional track in a fixed set of radii, and names them differently: Kato in millimeters (R370, R550…), Atlas and Bachmann in inches (15", 18"…). This page lists every plain curve radius each line offers, on one scale, so you can see which pieces are close to each other. The smallest piece a maker sells is not the tightest curve a locomotive is rated for — that is a separate statement, and we show it only where the maker itself publishes one.
The HO Code 83 vs Code 100 page sorts these makers' HO lines by rail code: Code 83, Code 100, or no Code number printed.
What the makers say about locomotives
Kato USA UNITRACK
Kato states that every Kato HO locomotive and car is designed to run through its R550 (550 mm) curve, the radius it calls the basic HO UNITRACK curve and the one that matches its #4 turnout.
Kato USA UNITRACK catalog (PDF), p. 32 · verified 2026-09-26Kato's catalog prints its own inch figures next to each radius, and they don't always agree between paragraphs (R370 appears as both 14 9/16 in. and 14 13/16 in.). The inch figures on this page are our own conversion (mm ÷ 25.4), not Kato's.
Every other line on this page shows not stated on the maker pages we checked in the locomotive column: the catalog and category pages we checked list the curve pieces only. Some individual locomotive product pages print a minimum radius for that one model; check the model's own page before planning track for it.
HO scale: curve radii by line
5 lines · 5 with the full category listing checked · 0 checked in part · 1 with a maker's locomotive statement. Counted from the table below — see method. Values in italics are our own conversion (1 in = 25.4 mm), not the maker's figure.
| Line | Curve radii listed | Smallest listed | Locomotive statement |
|---|---|---|---|
| Kato USA UNITRACK |
Kato USA UNITRACK catalog (PDF), p. 32 · verified 2026-09-26 Kato's HO catalog lists these as its 22.5-degree curve pieces. It also lists an R867 10-degree piece, which it describes as a supplement for building a siding off its #6 turnout, so it isn't counted as a separate curve size here. Kato USA UNITRACK catalog (PDF), p. 33 · verified 2026-10-05 These two are Kato's concrete-tie large-radius curve pieces, each an 11.25-degree section (half the angle of the 22.5-degree pieces above). The same catalog page also lists R730 and R790 concrete-tie pieces; those are the same radii as the R730 and R790 pieces already listed. | R370 Kato positions R370 as the tightest piece in the HO range, meant for layouts small enough to sit on a table, and R430 and R490 as small-layout sizes. It doesn't say which of its models will run on them. PDF p. 32 | R550 — see above |
| Atlas Code 83 snap track |
Atlas category page · verified 2026-09-26 Full-section item numbers 0530 (15"), 0532 (18"), 0535 (22"), 0536 (24"). The category also sells 1/3 and 1/2 sections of the same radii; those are shorter pieces, not extra radii. | 15" | not stated on the maker pages we checked |
| Atlas Code 100 snap track |
Atlas category page · verified 2026-09-26 Full-section item numbers 0831 (15"), 0833 (18"), 0836 (22"), 0837 (24"); half sections of 15" and 18" and a third section of 18" are also listed. | 15" | not stated on the maker pages we checked |
| Atlas True-Track (roadbed track) |
Atlas category page · verified 2026-09-26 Item numbers 0460 (18"), 0463 (22"), 0468 (24"). There is no 15" piece in this line. | 18" | not stated on the maker pages we checked |
| Bachmann E-Z Track, nickel silver |
Bachmann category page 1 of 4 · verified 2026-09-26 Page 1 of 4 of the category listing (items 1 to 21 of 69), including concrete-tie and bulk variants of the same radii. Bachmann category page 2 of 4 · verified 2026-09-26 Page 2 of 4 (items 22 to 42). The 28", 33.25" and 35.50" pieces are sold in 18-degree sections, and 33.25" also in 6- and 12-degree sections; Bachmann writes 35.50". Bachmann category page 3 of 4 · verified 2026-09-26 Page 3 of 4 (items 43 to 63): no plain curved pieces. Bachmann category page 4 of 4 · verified 2026-09-26 Page 4 of 4 (items 64 to 69): an 18" auto-reversing curved section, the same radius as page 1. | 15" | not stated on the maker pages we checked |
HO radius ladder
Every radius above in one list, tightest first. Pieces from different makers that sit close together are still different track — they are not interchangeable curves.
- 370 mm 14.6 in Kato USA UNITRACK
- 381 mm 15" Atlas Code 83 snap track
- 381 mm 15" Atlas Code 100 snap track
- 381 mm 15" Bachmann E-Z Track, nickel silver
- 430 mm 16.9 in Kato USA UNITRACK
- 457 mm 18" Atlas Code 83 snap track
- 457 mm 18" Atlas Code 100 snap track
- 457 mm 18" Atlas True-Track (roadbed track)
- 457 mm 18" Bachmann E-Z Track, nickel silver
- 490 mm 19.3 in Kato USA UNITRACK
- 550 mm 21.7 in Kato USA UNITRACK
- 559 mm 22" Atlas Code 83 snap track
- 559 mm 22" Atlas Code 100 snap track
- 559 mm 22" Atlas True-Track (roadbed track)
- 559 mm 22" Bachmann E-Z Track, nickel silver
- 610 mm 24" Atlas Code 83 snap track
- 610 mm 24" Atlas Code 100 snap track
- 610 mm 24" Atlas True-Track (roadbed track)
- 610 mm 24 in Kato USA UNITRACK
- 660 mm 26" Bachmann E-Z Track, nickel silver
- 670 mm 26.4 in Kato USA UNITRACK
- 711 mm 28" Bachmann E-Z Track, nickel silver
- 730 mm 28.7 in Kato USA UNITRACK
- 790 mm 31.1 in Kato USA UNITRACK
- 845 mm 33.25" Bachmann E-Z Track, nickel silver
- 902 mm 35.50" Bachmann E-Z Track, nickel silver
- 1546 mm 60.9 in Kato USA UNITRACK
- 1606 mm 63.2 in Kato USA UNITRACK
N scale: curve radii by line
5 lines · 5 with the full category listing checked · 0 checked in part · 0 with a maker's locomotive statement. Counted from the table below — see method. Values in italics are our own conversion (1 in = 25.4 mm), not the maker's figure.
| Line | Curve radii listed | Smallest listed | Locomotive statement |
|---|---|---|---|
| Kato USA UNITRACK |
Kato USA UNITRACK catalog (PDF), p. 15 · verified 2026-09-26 R117, R150 and R183 are sold under the name "Compact Curve Track". A curved deck-girder bridge at R448 is listed on the same page but is a bridge, not a plain track piece, so it is left out. | R117 | not stated on the maker pages we checked |
| Atlas Code 80 snap track |
Atlas category page · verified 2026-09-26 Item numbers 2510 (9 3/4"), 2520 (11"), 2525 (17"), 2526 (19"); half sections of 9 3/4" and 11" are also listed. | 9 3/4" | not stated on the maker pages we checked |
| Atlas Code 55 sectional track |
Atlas category page 1 of 2 · verified 2026-09-26 First page of the category listing (items 2010 to 2021). Atlas category page 2 of 2 · verified 2026-09-26 Second page of the same category listing (items 2022 to 2031). | 10" | not stated on the maker pages we checked |
| Atlas True-Track (roadbed track) |
Atlas category page · verified 2026-09-26 Item numbers 2410 (11"), 2412 (12.5"), 2414 (14"), 2416 (15.5"); a half section of 11" and 12.5" is also listed. | 11" | not stated on the maker pages we checked |
| Bachmann E-Z Track |
Bachmann category page 1 of 3 · verified 2026-09-26 Page 1 of 3 of the category listing (items 1 to 21 of 51); Bachmann writes 12.50", 15.50" and 17.50". Bachmann category page 2 of 3 · verified 2026-09-26 Page 2 of 3 (items 22 to 42): more variants of radii already on page 1. Bachmann category page 3 of 3 · verified 2026-09-26 Page 3 of 3 (items 43 to 51): more variants of radii already on page 1. | 11.25" | not stated on the maker pages we checked |
N radius ladder
Every radius above in one list, tightest first. Pieces from different makers that sit close together are still different track — they are not interchangeable curves.
- 117 mm 4.6 in Kato USA UNITRACK
- 150 mm 5.9 in Kato USA UNITRACK
- 183 mm 7.2 in Kato USA UNITRACK
- 216 mm 8.5 in Kato USA UNITRACK
- 248 mm 9 3/4" Atlas Code 80 snap track
- 249 mm 9.8 in Kato USA UNITRACK
- 254 mm 10" Atlas Code 55 sectional track
- 279 mm 11" Atlas Code 80 snap track
- 279 mm 11" Atlas True-Track (roadbed track)
- 282 mm 11.1 in Kato USA UNITRACK
- 286 mm 11.25" Atlas Code 55 sectional track
- 286 mm 11.25" Bachmann E-Z Track
- 315 mm 12.4 in Kato USA UNITRACK
- 318 mm 12.5" Atlas Code 55 sectional track
- 318 mm 12.5" Atlas True-Track (roadbed track)
- 318 mm 12.50" Bachmann E-Z Track
- 348 mm 13.7 in Kato USA UNITRACK
- 349 mm 13.75" Atlas Code 55 sectional track
- 356 mm 14" Atlas True-Track (roadbed track)
- 356 mm 14" Bachmann E-Z Track
- 381 mm 15" Atlas Code 55 sectional track
- 381 mm 15 in Kato USA UNITRACK
- 394 mm 15.5" Atlas True-Track (roadbed track)
- 394 mm 15.50" Bachmann E-Z Track
- 413 mm 16.25" Atlas Code 55 sectional track
- 432 mm 17" Atlas Code 80 snap track
- 445 mm 17.5" Atlas Code 55 sectional track
- 445 mm 17.50" Bachmann E-Z Track
- 476 mm 18.75" Atlas Code 55 sectional track
- 481 mm 18.9 in Kato USA UNITRACK
- 483 mm 19" Atlas Code 80 snap track
- 483 mm 19" Bachmann E-Z Track
- 508 mm 20" Atlas Code 55 sectional track
- 540 mm 21.25" Atlas Code 55 sectional track
- 718 mm 28.3 in Kato USA UNITRACK
- 777 mm 30.609" Atlas Code 55 sectional track
- 1803 mm 71" Atlas Code 55 sectional track
NMRA RP-11: degrees of curvature and minimum radius
The NMRA (National Model Railroad Association) publishes a recommended practice, RP-11, that sorts locomotives and cars into classes, E through Q, by size, and gives each class a minimum curve. For every class it prints the degrees of curvature, the prototype radius that goes with it, and the model radius in each scale. RP-11 aims these minimums at equipment running slowly, about 20 scale mph; for normal main-line speeds it says to use a higher class.
| Class | Degrees of curvature | Prototype radius | HO model radius | N model radius |
|---|---|---|---|---|
| E | 60° | 100 ft | 14 in / 356 mm | 7.5 in / 191 mm |
| G | 45° | 131 ft | 18 in / 457 mm | 10 in / 248 mm |
| I | 36.5° | 158 ft | 22 in / 559 mm | 12 in / 305 mm |
| L | 30° | 193 ft | 26.5 in / 673 mm | 14.5 in / 368 mm |
Both the inch and the millimeter figures are printed in RP-11; we have not converted them. We do not convert between degrees and radius either: the figures above are RP-11's own. RP-11 also notes that some models, entry-level ones in particular, run on tighter curves than this, and that detailed brass models may need wider ones. The other classes, the other scales and the turnout sizes are in the full document: NMRA RP-11 (PDF), p. 3 · verified 2026-10-12.
Known gaps
- The smallest curve a manufacturer sells is not the same thing as the tightest curve a given locomotive can run on. Only Kato publishes a locomotive statement in the sources checked here, and only for HO.
- Atlas and Bachmann locomotive product pages sometimes print a minimum radius for that model. This page does not collect those per-model figures yet.
- Flex track (Atlas Super-Flex, Bachmann flex) can be bent to radii not listed here and is left out of this comparison.
- Radii are listed as each manufacturer names them. Different manufacturers may measure radius to a slightly different point on the track; none of the sources checked here say which point they use.