Roco geoLine: what baseboard size do you need?
Benjamin | TrackDrawer.com · published 13 November 2026
For a closed loop in Roco geoLine you need a 90 x 90 cm baseboard, on R2 at 358 mm, the tightest curve in the system. A loop with a passing loop fits from 165 x 90 cm, and from 120 x 105 cm the Auto-designer lays double track on R3 and R2. On 240 x 120 cm it becomes double track on R4 and R3 with a siding and a yard: 11.48 m of track.
We measured this with the TrackDrawer Auto-designer, using an ordinary collection of geoLine and a 5 cm clear margin around the baseboard.
Three radii on a fixed roadbed
Roco geoLine is H0 track for two-rail DC on a fixed roadbed. The pieces click together and stay put on a table or carpet; a baseboard is not required, but it helps as soon as the layout stays up. The roadbed is about 38.5 mm wide in our catalogue.
There are three curve radii: R2 at 358 mm, R3 at 434.5 mm and R4 at 511.1 mm. geoLine has no R1; the numbering follows Roco Line, where R2 has the same radius. The radii are 76.5 mm apart, which is the geoLine track spacing. How geoLine differs from Roco Line and from Piko A-Gleis is covered in Roco geoLine or Roco Line and Piko A-Gleis or Roco geoLine.
Outside size per radius
The outside size of a circle is twice the radius plus the width of the roadbed. For the baseboard we add a 2 x 50 mm margin.
| Radius | Radius in mm | Outside of circle | Baseboard with 5 cm margin |
|---|---|---|---|
| R2 | 358 mm | 754.5 mm | 85.5 cm |
| R3 | 434.5 mm | 907.5 mm | 100.8 cm |
| R4 | 511.1 mm | 1060.7 mm | 116.1 cm |
Each step outwards costs a little over 15 cm of depth. Double track on R3 and R2 ends up just over a metre with the margin, on R4 and R3 over 1.15 m.
The smallest loop: 90 x 90 cm
With 85.5 cm as the lower limit, that becomes a 90 x 90 cm baseboard in 5 cm steps. The designer joins twelve R2 curves (61122) into a circle there: 12 pieces and 2.25 m of track, with no room for straights. On 100 x 90 cm it becomes an R2 oval with 14 pieces and 2.45 m.
A passing loop: from 165 x 90 cm
The geoLine turnout (61140 left, 61141 right) is 200 mm long and diverges at 22.5 degrees with a 502.7 mm radius. The compensating curve 61128 has the same radius and angle; that radius exists only for this curve and is not available as an ordinary curve. Turnout and curve together advance 384.75 mm; on the straight side, the 185 mm straight 61111 makes it up to 385 mm.
The Auto-designer found the first loop with a passing loop on 165 x 90 cm: "Station with two platforms on R2, plus 2 sidings", 30 pieces and 5.58 m of track. At 100 cm deep too, 165 cm remained the smallest width. How a passing loop is built is explained in passing loop: how two trains pass each other.
What fits on common sizes?
| Baseboard | What fits (examples) | Pieces | Track |
|---|---|---|---|
| 90 x 90 cm | circle on R2 | 12 | 2.25 m |
| 100 x 90 cm | R2 oval | 14 | 2.45 m |
| 165 x 90 cm | station with two platforms on R2, plus 2 sidings | 30 | 5.58 m |
| 180 x 90 cm | R2 oval, plus a siding and a yard | 32 | 5.63 m |
| 120 x 105 cm | double track R3/R2 | 28 | 5.72 m |
| 140 x 105 cm | double track R3/R2, plus a siding and a yard | 38 | 7.48 m |
| 160 x 105 cm | double track R3/R2, plus a siding and a yard | 44 | 8.60 m |
| 200 x 120 cm | double track R3/R2, plus a passing loop and a yard | 57 | 10.59 m |
| 240 x 120 cm | double track R4/R3, plus a siding and a yard | 59 | 11.48 m |
What stands out:
- At 90 cm deep you get one loop. On 180 x 90 cm the designer chose an oval with a siding and a yard as the longest variant; a station with two platforms comes almost as far (5.58 m).
- 15 cm of extra depth makes the difference. At 105 cm deep double track fits from 120 cm wide, and every extra 20 cm of width adds more than a metre of track.
- On 240 x 120 cm everything moves out one radius. The double track then runs on R4 and R3, which is smoother with long coaches. How that compares with the other H0 systems is covered in an H0 layout on 240 x 120 cm.
A small range, used cleverly
geoLine has fifteen items in our catalogue. That is not many, but it works because the dimensions are matched to each other:
- Four straight lengths. 200 mm (61110), 185 mm (61111), 100 mm (61113) and 76.5 mm (61112). The last one is exactly one track spacing long.
- Short curves. R2 and R3 also come as 7.5 degree pieces (61129 and 61130). With them you can fill an angle that is not a multiple of 30 degrees.
- Turnouts with built-in motors. Besides the standard turnouts there is a three-way turnout (61160) and a double slip (61164), all at 22.5 degrees. Our catalogue has no separate diamond crossing; two tracks cross via the double slip.
geoLine has no flexible track. If you want free-form curves or a wider radius than R4, you will end up with a different system.
Frequently asked questions
Does double track fit on a baseboard one metre deep?
Only just not with a 5 cm margin: double track on R3 and R2 is 907.5 mm wide on the outside, 100.8 cm with the margin. The designer laid the first double track on 120 x 105 cm, with 28 pieces and 5.72 m of track.
Can I use geoLine and Roco Line together?
They share R2 at 358 mm, but the other radii, the track spacing and the roadbed differ. For the size of your baseboard, plan with whichever system provides most of the pieces.
Your own baseboard
Enter your baseboard and your geoLine and let the Auto-designer lay a plan that fits.