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What is the difference between HO and OO scale

Helpful Guides at Little Train Shop

What is the difference between 
HO and OO Scale

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HO and OO Scale are the most common scales in the model railway hobby as they offer the largest number of products to the hobbyist. However, the two names, and being interchanged with each other, often causes some confusion as to what the differences are and if they are compatible with one another.

It’s important to note that both HO and OO Scale are compatible with each other as they share the same gauge of track (16.5mm, which is the distance between the rails). This means you can interchange locomotives, rolling stock, track and accessories of both scales and won’t experience any running concerns.

The difference between the two scales comes down to size. HO Scale models are built to 1:87th scale, meaning 87 packed together will in effect be the same size of the real thing. This is the correct scale for 16.5mm gauge track. OO Scale models are built to 1:76th scale (again, 76 crammed together will recreate the same height), however, this is not true to scale when using 16.5mm gauge track.

The main differences modellers will spot between the two scales is size (but sometimes it takes a fine eye to pick it). OO Scale will appear slightly larger to HO Scale models and accessories.

OO SCALE

SCALE

RATIO

GAUGE

4mm to 1ft

1:76

16.5mm

OO Scale is the most popular scale produced in the United Kingdom and is commonly referred to as 4mm scale. This scale is used by manufacturers including Hornby, Bachmann Branchline, Dapol and Oxford Rail.

DIFFERENCES BETWEEN HO SCALE:

Larger in size in comparison to HO, and not prototypically correct.

 

HO SCALE

SCALE

RATIO

GAUGE

3.5mm to 1ft

1:87

16.5mm

HO Scale is the most popular scale produced in across the World and is commonly referred to as 3.5mm scale. This scale is used by manufacturers including Atlas, Auscision, Austrains, Bachmann, Eureka, Faller, Frateschi, Kato, Lima, Noch, Powerline, Walthers and Woodland Scenics (plus a whole host).

DIFFERENCES BETWEEN OO SCALE:

Smaller in size in comparison to OO, and correct scale to rail gauge.

 

FAQ: CAN I USE HO AND OO SCALE TRACK TOGETHER?

Yes, you can. Both use the same Gauge, which is 16.5mm.

FAQ: CAN I USE HO AND OO LOCOMOTIVES AND ROLLING STOCK TOGETHER?

Yes, you can, but you may need to fit alternative couplings to rolling stock and locomotives so that they will connect together. OO Scale manufacturers predominantly use the tension lock style of coupling, whereas HO Scale manufacturers choose to use more prototypical knuckle type couplings.

FAQ: WHICH SCALE IS BETTER?

This is personal preference. OO Scale is predominately seen across British models and layouts, whereas HO Scale is predominately seen across American, Australian and European models and layouts.

FAQ: WHY ISN’T THERE JUST ONE SCALE INSTEAD OF TWO?

OO Scale has been well established in the British market for several decades and has become the norm. While a few manufacturers in Britain have tried to push towards a HO scale, this hasn’t been a welcomed addition and OO Scale continues to thrive.