A TT layout on 140 x 70 cm: what fits?
Benjamin | TrackDrawer.com · published 6 November 2026
A 140 x 70 cm baseboard in TT takes one loop on the tightest curve, R01 at 267 mm, with a passing loop, sidings or a small two-platform station inside it. The Auto-designer already found a loop with a passing loop on 120 x 70 cm; the extra 20 cm mainly give longer tracks. A second, wider loop does not fit at 70 cm deep.
Why 70 cm of depth sets the limit
TT is 1:120 scale on 12 mm track. In our catalogue that is Tillig TT, track without roadbed, 20 mm wide seen from above. The curves are 43 mm apart: R01 267 mm, R11 310 mm, R21 353 mm and R31 396 mm.
A loop is twice the radius plus the track width across:
| Radius | Radius in mm | Loop outside width | Board with 5 cm margin |
|---|---|---|---|
| R01 | 267 mm | 554 mm | 65.4 cm |
| R11 | 310 mm | 640 mm | 74.0 cm |
| R21 | 353 mm | 726 mm | 82.6 cm |
| R31 | 396 mm | 812 mm | 91.2 cm |
At 70 cm deep with a 5 cm margin, 600 mm is left for the loop. R01 fits with 46 mm to spare; R11 is already 640 mm across and no longer fits. Double track with R11 on the outside therefore needs at least 74 cm. The smallest board with a closed loop in TT is 70 x 70 cm in our measurement; how that compares with H0, N and Z is covered in H0, N, TT or Z.
What the Auto-designer lays on it
We had the Auto-designer work on 140 x 70 cm and on 120 x 70 cm, with a 5 cm margin and a typical box of Tillig TT: per radius a full circle plus four curves, eight of each of the first six straight lengths, three left and three right turnouts, four matching curves and four make-up pieces. It searched with three goals: continuous running, several trains with a station, and variety.
| Board | Variant | Pieces | Track | Passing loops | Sidings |
|---|---|---|---|---|---|
| 140 x 70 cm | R01 oval, plus siding and yard | 59 | 4.51 m | 0 | 3 |
| 140 x 70 cm | R01 oval with passing loop, plus 2 sidings | 57 | 4.42 m | 1 | 2 |
| 140 x 70 cm | R01 oval with passing loop, plus yard | 51 | 4.34 m | 1 | 2 |
| 140 x 70 cm | Station with two platform roads on R01 | 48 | 3.94 m | 2 | 0 |
| 120 x 70 cm | R01 oval, plus siding and yard | 48 | 3.59 m | 0 | 3 |
| 120 x 70 cm | R01 oval, plus 2 sidings | 46 | 3.47 m | 0 | 2 |
| 120 x 70 cm | R01 oval with passing loop, plus yard | 36 | 3.42 m | 1 | 2 |
| 120 x 70 cm | Station with two platform roads on R01 | 32 | 3.15 m | 2 | 0 |
What you learn from it:
- Everything sits on R01. At 70 cm deep the tightest curve is the only one that fits. That holds for every variant.
- A passing loop already fits on 120 cm. On 120 x 70 cm the designer laid an oval with a passing loop, also with a yard beside it, and a station with two platform roads, where two trains can wait for each other on both sides of the oval. On 140 cm the same layouts get longer: the oval with passing loop and yard grows from 3.42 to 4.34 m, the two-platform station from 3.15 to 3.94 m.
- Many pieces for few metres. 59 pieces for 4.51 m of track: TT track pieces are short (the longest straight is 166 mm), and sidings and yards are built from many small pieces.
The Tillig TT turnout pattern
Tillig does not make a separate matching curve for its TT turnouts. In our catalogue the designer therefore uses an ordinary curve: the standard EW2 turnout (83331 right, 83332 left) is 166 mm long and diverges at 631 mm over 15 degrees; it is followed by the R32 curve, 396 mm over 15 degrees. Together they move 265.81 mm forward and put the second track 34.99 mm beside the first. On the straight side you make up the length with short straights (G5 at 36.5 mm, G6 at 21.3 mm and G4 at 41.5 mm).
That passing loop therefore sits closer to the main line than two circles do (43 mm), but still above the NEM minimum for TT of 34 mm. What those distances mean is explained in track spacing.
Tillig also has a shorter turnout, EW1 at 129.5 mm diverging at 353 mm, and a slimmer EW3 of 207 mm at 984 mm over 12 degrees. With flexible track (83125, about 664 mm) you can bend the connections yourself.
Train length on 140 cm
A 26.4 m coach is about 220 mm long at 1:120; TrackDrawer uses a 181 mm standard wagon for TT. At 140 cm wide, the straight between the two R01 half circles is about 140 - 10 - 2 x 27.7 = 74.6 cm per long side. After two turnouts with their curves (26.6 cm each), about 21 cm of clear platform road remains. A station on 140 cm therefore suits a locomotive with one or two short wagons, or trains that stand partly in the curve. On 120 cm the straight is only 54.6 cm: the two turnouts with their curves lie almost back to back there, leaving hardly any clear platform road.
A tight 267 mm curve and long coaches do not go well together in TT either: how far a vehicle swings out in a curve is worked out in the tightest curve radius in N; the principle is the same in TT.
A board you can carry
A 140 x 70 cm board is big enough for proper continuous running and small enough to sit on a desk or a cabinet. At 70 cm deep you can reach the back from one side, so the board can stand against a wall. With a light frame two people can carry it, and you can put it away when you are not using it.
Frequently asked questions
Does double track fit on 140 x 70 cm in TT?
No. The second loop has to be on R11 or wider, and that is already 64 cm across. With a 5 cm margin you need at least 74 cm of depth.
Is 140 x 70 cm in TT comparable to 180 x 90 cm in H0?
Roughly. In both cases one loop on the tightest curve fits, with a passing loop or sidings; see an H0 layout on 180 x 90 cm. TT trains are only about 73 percent as long, though, so your station feels roomier.
Try it yourself
Enter your own TT track and let the Auto-designer show what fits on your baseboard.