HO Scale (1:87) Calculator & Conversion Chart
Most popular worldwide · 1.15% of real size
HO — "half O," 1:87.1 — is the world’s most popular model railway scale, with the deepest catalog of locomotives, structures, and scenery of any scale in any hobby. Its 3.5 mm-to-the-foot maths makes metric conversion unusually clean.
Precision Scale Conversion Calculator
HO Scale (1:87) Quick Facts
- 1 real foot = 0.138″ (3.5 mm) on the model
- 1 real meter = 11.49 mm on the model
- A 6 ft (183 cm) person = 21 mm (0.83″) tall
- Model is 1.15% of real size — use this as the scale percentage in 3D-print slicers
HO Scale (1:87) Reference Chart
| Real Size | mm | cm | inches |
|---|---|---|---|
| 1 inch | 0.292 mm | 0.029 cm | 0.011″ |
| 1 foot | 3.5 mm | 0.35 cm | 0.138″ |
| 6 ft (person) | 21 mm | 2.1 cm | 0.828″ |
| 1 meter | 11.5 mm | 1.15 cm | 0.453″ |
| 3 m (room height) | 34.5 mm | 3.45 cm | 1.358″ |
| 10 meters | 114.9 mm | 11.49 cm | 4.525″ |
| 30 m (building) | 344.8 mm | 34.48 cm | 13.576″ |
Frequently Asked Questions
What is HO scale in mm, cm, and inches?
In HO Scale (1:87), 1 unit on the model equals 87 of the same unit in real life. One real foot equals 0.138 inches (3.5 mm) on the model, one real meter equals 11.49 mm (1.15 cm), and the model is 1.15% of real size.
How tall is a 6 ft person in HO Scale (1:87)?
A 6-foot (183 cm) person stands 21 mm (0.83 inches) tall in HO Scale (1:87).
How do I convert a real measurement to HO Scale (1:87)?
Divide the real measurement by 87. For example, a 10 m object is 114.9 mm long in HO Scale (1:87). The calculator on this page does this automatically in both directions.
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