OO Scale to HO Scale Conversion
HO and OO share the same 16.5 mm track gauge despite being different body scales (1:87 vs 1:76.2), a quirk that goes back decades of British modelers running OO stock on HO track. Converting between them tells you how much larger OO locomotives and figures will look next to HO scenery and structures built to the "correct" gauge-matched scale.
To convert a model dimension from OO Scale (1:76) to HO Scale (1:87), multiply it by 0.8736 (76 ÷ 87). The result is a smaller model — every length, width, and height changes by the same factor.
Conversion Chart
| OO Scale size (mm) | HO Scale size (mm) |
|---|---|
| 1 mm | 0.87 mm |
| 2 mm | 1.75 mm |
| 5 mm | 4.37 mm |
| 10 mm | 8.74 mm |
| 20 mm | 17.47 mm |
| 50 mm | 43.68 mm |
| 100 mm | 87.36 mm |
Frequently Asked Questions
How do I convert OO Scale to HO Scale?
Multiply any OO Scale model dimension by 0.8736 to get the HO Scale dimension. This works because OO Scale is 1:76 and HO Scale is 1:87, so the factor is 76 ÷ 87 = 0.8736.
Is HO Scale bigger or smaller than OO Scale?
HO Scale models are smaller: the same subject is only 0.8736× the size in each dimension compared to OO Scale.
Keep Exploring
Reverse: HO Scale to OO Scale · OO Scale (1:76) guide · HO Scale (1:87) guide · Full calculator