Model railway minimum curve conundrum – what’s the smallest radius?

What’s the minimum curve radius for model railways? The numbers you need to know for Z, N, OO and HO track from Peco, Hornby, Märklin.

Nothing else impacts a layout design or track plan as much as the minimum radius of the curves. You want them as tight as possible to get in as much track as you can in the space available but equally go too sharp and you’ll limit the speed your trains can go at around the bends, how long your trains can be and even the realism of your track.

Extra: If you are constructing a layout in a small space and have to use tight curves but are concerned about the look, hide the tightest curves in hills or behind trees etc and then have the visible part in a larger radius. You can also improve the look of curves using superelevation.

I’ve listed the minimum radii for the most common UK track gauges are shown below. Double these numbers for the diameter of a curve if going all the way around, creating a semi-circle to bring the track back in the direction it comes from for example.

Z Gauge
6 inches/150mm (Märklin)

N Gauge
9 inches/228mm (Peco, No 1 curve; Fleischmann’s equivalent is tighter at 7.6inches/193mm)

OO Gauge
14.6inches/371mm (Hornby & Peco No 1 radius).

HO Gauge
15 inches/380mm (Atlas track).

Remember that you’ll need to slow down your trains for corners (just as real trains do) and that longer locomotives and rolling stock won’t work on these so wider curves will be needed if you have large trains — only shorter wheelbase locomotives and rolling stock (4 wheel wagons etc) will manage these minimum curve radii.

Ideally, use larger radius 2 or 3 sections (or even radius 4 in the case of OO) if possible and always try to have a larger radius at the entry to the curve (known as an easement) as this will help the train as it enters the curve.

> A final, personal, note: I spend a huge amount of time testing, photographing, writing and researching techniques for these articles and pay for all the running costs of MRE out of my own pocket. If you found this article useful you can support me by making a donation on my fund-raising page. Thanks and happy modelling, Andy.
  1. Hi Andy,
    Now I am planning my Z gauge scenario . But I am confused that Marklin locos can run on Rakuhan minimum radii track (145mm) ?

    • Hi Bear, It’s really down to the wheel base of your fixed axel rolling stock. Rolling stock with axles on the bogies should be okay. The shorter the wheel base on fixed axel locos and rolling stock, the tighter the curves they’ll be able to handle. For curves of 145mm I’d be surprised if anything but the shortest Marklin locos will manage it, the 220mm curves (R004 I think) would be safer. Does this help? Come back to me if you have more questions. Andy

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