The Pros And Cons of OO Scale vs TT120

OO vs TT:120: which should you choose?

OO has been the standard British scale for generations. TT:120 is the newcomer: Hornby and Peco brought it to the UK in 2022, and the range has grown every year since. Trenton is built in OO, so I’ll say up front where my own experience lies, but TT:120 deserves a fair look.

The basics

OO is 1:76 scale running on 16.5mm track. TT:120 is 1:120 scale on 12mm track, which makes the models roughly two-thirds the size of OO. Don’t confuse it with the older British TT of the 1950s and 60s, which was 3mm scale; the two are not compatible.

Why choose TT:120

1. Space. A layout that needs a garage in OO can fit a spare room in TT:120. This is the main reason people choose it.
2. Easier to handle than N gauge, with more presence, while still saving a lot of space over OO.
3. Scale and gauge match. OO models are slightly too big for their track; TT:120 track is the correct width for the scale.
4. A growing range. Hornby now offers steam and diesel locomotives, coaches, wagons, train sets and buildings, and added more in 2026, including a Black 5 and Class 31. Peco supplies track.

Why TT:120 might not suit you

1. Far less choice. The range is growing but is still a fraction of what OO offers, and it comes mostly from one manufacturer. If you want a specific locomotive or era, check it exists first.
2. Almost no second-hand market, because the scale is so new.
3. Fewer kits, detailing parts and scenic accessories made for the scale.
4. A smaller community, so fewer clubs, layouts to visit and people to ask.

Why choose OO

1. Choice. Nearly every British locomotive class of note has been made in OO, by several manufacturers, in most liveries and eras.
2. A huge second-hand market, which keeps costs down when you’re starting out.
3. Everything else is made for it: buildings, vehicles, figures, kits and 3D print files.
4. Most British clubs, exhibitions and magazines are centred on OO.

Why OO might not suit you

1. Space. Realistic curves and train lengths need room, and a main line in OO soon fills a garage.
2. Larger layouts cost more to build and take longer to finish.

So which?

If space is your limit and you’re happy with what’s currently made, TT:120 is a serious option and is getting better each year. If you want a particular period, region or locomotive, or you like hunting for bargains, OO is still the safer choice. I chose OO for Trenton because 1970s BR Blue in the East Midlands needs models that only OO offers in depth.