Gradients: how steep can a model train climb?
Benjamin | TrackDrawer.com · published 6 November 2026
An ordinary model train handles a 3 % gradient without trouble, and that is the limit TrackDrawer checks by default. For long trains or weak locos, stay at 2 %; above 4 % it becomes a matter of short trains and strong locos. The real problem is rarely the percentage but the length: to climb 70 mm in H0 at 3 %, you already need 2.33 m of track.
What a percentage means
A 3 % gradient rises 3 mm for every 100 mm of track, or 3 cm per metre. The percentage is the same in every scale: 3 % is as steep in N as in H0. What does differ is how high you have to go. A bridge, or a track above another track, has to leave room for the train underneath, and that train is much taller in H0 than in N. So the same crossing needs far less gradient in N than in H0.
How high is high enough depends on the structure gauge: the space that must stay clear around the track. Following NEM 102, TrackDrawer works in H0 with about 55 mm of clear space above the top of the rail without overhead wires and 65 mm with them, scaled in proportion for the other scales. On top of that comes the thickness of whatever lies above: the rail itself and the bridge deck or trackbed.
How much length you need
The length of a gradient is the height divided by the percentage. For the table we take, per scale, the clear space without overhead wires, the rail height TrackDrawer uses by default and a 10 mm deck. The top row is the standard clearance of 70 mm that TrackDrawer checks.
| Scale | Clear space | Height to climb | Length at 2 % | At 3 % | At 4 % |
|---|---|---|---|---|---|
| TrackDrawer default | 70 mm | 3.50 m | 2.33 m | 1.75 m | |
| H0 | 55 mm | 71.6 mm | 3.58 m | 2.39 m | 1.79 m |
| OO | 63 mm | 80.5 mm | 4.03 m | 2.68 m | 2.01 m |
| TT | 40 mm | 54.8 mm | 2.74 m | 1.83 m | 1.37 m |
| N | 30 mm | 43.6 mm | 2.18 m | 1.45 m | 1.09 m |
| Z | 22 mm | 34.6 mm | 1.73 m | 1.15 m | 0.87 m |
That is pure climb, without the transitions at the start and the top (more on those below). A few consequences:
- A gradient rarely fits on one straight. On a 240 x 120 cm baseboard, a 5 cm edge leaves 2.30 m of length. A 70 mm climb at 3 % is already longer than that. In H0 a gradient therefore almost always runs through a curve. What else fits on that board is covered in an H0 layout on 240 x 120 cm.
- On a small board, half the layout climbs. An oval on R1 in Märklin C track is 4.11 m long. If the track has to pass 70 mm above itself somewhere, more than half of that loop is gradient, and it still has to come back down.
- N and Z really do save space. In N the climb is about 60 % of the H0 figure. A two-level crossing becomes feasible much sooner.
If you have no room for such a long gradient, you can stack the height in a spiral: see the helix.
Why 3 % and not more
A loco pulls through the friction of its wheels on the rail. On a gradient it also has to lift the weight of the whole train. The steeper the climb, the bigger that share, until the wheels slip or the speed drops so far that it no longer looks like a railway. Locos with traction tyres or several driven axles hold out longer; light locos and long passenger trains struggle first.
Three things make a gradient harder than the percentage suggests:
- A curve. In a curve the wheel flanges rub against the rail and slow the train further. A gradient in a tight curve feels steeper than the same gradient on a straight. Keep it a little gentler there.
- Train length. Every extra coach is extra weight. A train that just makes 3 % will not make it with two more coaches.
- Going down. On a descent the train pushes the loco. With analogue control it speeds up, and the couplings are under pressure. An even gradient without sudden kinks helps here too.
Test with your heaviest train before you fix the gradient for good: lay the track loose on a plank at the intended angle and run it up and down a few times.
The transition: no kink
Track that goes from level to 3 % in one step forms a kink. Long vehicles ground there with their middle or their ends, couplings lift and uncoupling becomes likely. Let the gradient build up gradually over about two track pieces: gentle first, then the full gradient, and gently back to level at the top.
Never put a turnout on or right next to such a transition either. A turnout that is not quite level is a classic cause of derailments; see train derails at the turnout.
Gradients in TrackDrawer
In the Height panel, switch on "Gradients and bridges". You set three things there: the maximum gradient (3 % by default), the minimum clearance between two tracks above each other (70 mm by default, meant for H0) and the transition length (200 mm by default). If you model in N or Z, set the clearance lower.
Then you enter heights, per connection point of a piece. It is quicker with "Distribute gradient": pick the first and last piece of a run, enter the end height, and TrackDrawer spreads the climb evenly and shows the percentage in green or red. The panel also gives the rule of thumb straight away: for 70 mm clearance at 3 % you need about 2.3 m of gradient.
The check then watches the whole plan:
- Too steep: a piece that climbs more than your maximum gets an error.
- Kink: if the gradient of two adjoining pieces differs by more than three quarters of your maximum (so more than 2.25 percentage points at 3 %), you get a warning to lay a longer transition.
- Too low: if two tracks cross with less height difference than the clearance, that is an error.
- Height difference at a joint: if two pieces meet at different heights, the check reports the difference in millimetres.
In 3D you see the gradient for real and can run a train over it. A ready-made example is the figure of eight with a bridge, where the Auto-designer works out the gradient itself: see the figure of eight. Plans with gradients and bridges are saved with Pro. Draw your layout in the app and see straight away whether your climb stays under 3 %.
