HO Scale to OO 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 HO Scale (1:87) to OO Scale (1:76), multiply it by 1.1447 (87 ÷ 76). The result is a larger model — every length, width, and height changes by the same factor.
Conversion Chart
| HO Scale size (mm) | OO Scale size (mm) |
|---|---|
| 1 mm | 1.14 mm |
| 2 mm | 2.29 mm |
| 5 mm | 5.72 mm |
| 10 mm | 11.45 mm |
| 20 mm | 22.89 mm |
| 50 mm | 57.24 mm |
| 100 mm | 114.47 mm |
Frequently Asked Questions
How do I convert HO Scale to OO Scale?
Multiply any HO Scale model dimension by 1.1447 to get the OO Scale dimension. This works because HO Scale is 1:87 and OO Scale is 1:76, so the factor is 87 ÷ 76 = 1.1447.
Is OO Scale bigger or smaller than HO Scale?
OO Scale models are larger: the same subject is 1.1447× bigger in every dimension in OO Scale than in HO Scale.
Keep Exploring
Reverse: OO Scale to HO Scale · HO Scale (1:87) guide · OO Scale (1:76) guide · Full calculator