Hobbies · Model railroading
Model railroad riser calculator.
Pick a grade, say how far apart your risers are, and the calculator lists the height of every riser along the run. Or enter the height you must clear and it returns the length of grade needed. Example: in HO, clearing a Modern-era overpass takes 3.17 inches of NMRA clearance plus 0.5 inch of deck. At 2% that needs 183.4 inches, about 15.3 feet.
Your numbers
Result
Working out the result.
How the risers are calculated
A grade is the rise divided by the run, as a percentage. So the rise over any run is the run times the grade, and the run needed for a rise is the rise divided by the grade. A 2% grade rises 2 inches in every 100 inches, or 0.02 inch per inch. The riser table is the same sum at every spacing you choose: the height at distance x is x times the grade. The last row is the end of the run, even when it falls between spacings.
For the overpass mode, the height to clear comes from NMRA RP-7.1, Tangent Track Centers and Clearance Diagrams (2019), dimension H, the clearance height for bridges and obstacles measured from the top of the railheads. RP-7.1 gives H as 17 feet for the Old-Time/Narrow Gauge era, 22 feet for Classic and Early Modern, and 23 feet for Modern. The calculator scales those by your scale ratio from NMRA S-3.2: in HO that is 2.34, 3.03, 3.03 and 3.17 inches. It adds the thickness of the deck, which you measure on your own layout. The NMRA index lists no standard on model railroad grades, so this tool does not claim a maximum grade.
Worked examples with real numbers
- HO, 2% grade over 50 inches. The rise is 1.0 inch. With risers every 10 inches the heights are 0.2, 0.4, 0.6, 0.8 and 1.0 inch.
- Clearing a Modern-era overpass in HO. NMRA height 3.17 inches (23 feet at 1:87.1) plus 0.5 inch of deck is 3.67 inches. At 2% the run is 183.4 inches, about 15.3 feet. At 3% it is 122.3 inches, about 10.2 feet.
- The same in N. 23 feet at 1:160 is 1.725 inches, so 0.5 inch of deck makes 2.225 inches and the run at 2% is 111.25 inches.
What this calculator leaves out
It assumes one constant grade. A real grade needs easing at both ends, which the vertical transition calculator handles. It does not know the thickness of your roadbed and subroadbed, so measure it. It does not check that your locomotives can climb the grade you choose.
Frequently asked questions
How do I work out riser heights for a grade?
Multiply the distance from the start of the grade by the grade as a fraction. At 2%, a riser 30 inches along the grade stands 0.6 inch above the start.
How long a ramp do I need to get over another track?
Divide the height to clear by the grade. The calculator uses the NMRA RP-7.1 clearance height for your scale and era plus the deck thickness you give. In HO, Modern era, with 0.5 inch of deck, that is 3.67 inches, or 183.4 inches at 2%.
What clearance does the NMRA recommend above the rail?
NMRA RP-7.1 gives dimension H as 17 feet for Old-Time, 22 feet for Classic and Early Modern, and 23 feet for Modern, measured from the top of the railhead. In HO that is 2.34, 3.03, 3.03 and 3.17 inches.
What grade should a model railroad use?
The NMRA index lists no standard on grades, so this tool does not set one. Test your own trains on a short section before building the whole ramp.
Do I measure grade along the track or along the floor?
The calculator treats the run as the length along the grade. At model grades the difference from the horizontal is very small.
Why does the last row not match my spacing?
The table always ends at the end of your run. If the run is not a multiple of the spacing, the final row is the end of the run.
Sources
Retrieved
- NMRA RP-7.1: Tangent Track Centers and Clearance Diagrams (2019) — clearance dimension H by era (read 2026-10-26)
- NMRA S-3.2: Track, Standard Scale (28 June 2026) — scale ratios (read 2026-10-26)
- NMRA index of Standards and Recommended Practices — checked for any standard on grades: none listed (read 2026-10-26)
Geometry and NMRA clearance heights
Not affiliated with the NMRA. The standards were read on 26 October 2026. Nothing you type is sent or stored.