Fitting a model railway into your space

Most layouts start with a space at home. It might be a table, a board under the bed or a corner of the loft. The curves decide how much of that space the track needs. The sizes below are quoted from Hornby's own track pages, read on 19 October 2026.

What "2nd radius" means

Hornby sells its curved set-track in numbered sizes, called 1st radius, 2nd radius and so on. The number is a label. The size in millimetres is on the page for each piece.

For TT:120, Hornby says the radius is measured to the centre of the running rails. It recommends allowing an extra 10mm when you work out how much space you need.

Hornby OO curves

Hornby's two 4th radius pages describe the curve in different ways. The double curve page (R8262) says With a 572mm arc spanning 45° and measuring 450mm in length. The single curve page (R8261) says Radius: 4 (235mm) and also 235mm in length. If you plan around 4th radius curves, measure a piece you own first.

Hornby's OO straight (R600) is 168mm long. Its page lists the piece as 2.9cm wide.

Hornby TT:120 curves

Hornby says its TT:120 track has a gauge of 12mm. It spaces parallel tracks about 43mm apart, centre to centre, and calls this "Standard Track Centres". It also says the TT:120 Track Pack extended layout needs a board of 54" x 40" (137cm x 102cm).

A quick check for a circle

A full circle is twice the radius across, measured from the centre of the rails on one side to the centre on the other. So a circle of Hornby OO 2nd radius, at 438mm, is twice that across. The track itself is wider than its centre line, and Hornby lists its OO track as 2.9cm wide, so add that too.

An oval adds its straights to the length. Each OO straight adds 168mm. Leave a margin at the edge of the board as well.

Hornby's train set pages list a "Space Required" value and a "Minimum Curve". One OO starter set read today lists 94 x 77cm, with 1st radius curves.

Where the layout goes

Hornby's TT:120 guide calls a sheet of plywood possibly the simplest baseboard. It names 6' x 4' and 8' x 4' as the most common sizes, and suggests ½" (12mm) thick sheets. It recommends gluing and screwing 2" x 1" battens round the underside, with bracing across the centre about every 15".

The same guide asks you to leave room to reach every part of the layout. People need to clean the track, put derailed trains back, and still open the windows and doors. It says the loft is a favourite place in the UK, and warns that a loft or garage swings between hot and cold unless it is insulated.

The NMRA's beginner's guide makes a similar point about planning. It says freehand track plans tend to be optimistic about how much track fits, and that most of us fudge the curve radius.

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