The key thing to remember when trying to figure out scales, is the lower the number after the: the bigger the size of the toy.
Horse 1:9 Scale
The largest and most popular model size available, with horses roughly measuring 20cm high by 6cm wide by 32cm long. Traditional Series models are for play, collecting, showing and more! They are beautifully hand crafted and usually packaged in colorful window boxes.
Horse 1:12 Scale
These are a bit smaller than the Traditional 1:9 scale, with horses roughly measures 15cm high by 5cm wide by 22cm long. The recommended age on this group is 4 years and up. These horse are also hand crafted, but their models and accessories are geared to the slightly younger horse lover, giving them excellent play value. As a rule they are priced more affordably than the more collectable Traditional Series.
Horse 1:16 Scale
This is rather a limited range of very solid horses, with a typical horse roughly measuring 14cm high by 4cm wide by 18cm long. The Bruder horse lorry and the horse box are great quality, and there is a horse stable, field shelter, fences, some new riding accessories and people. Britains Big Farm have just brought out a horse box with horse and foal, so may be adding to their horse range too.
Horse 1:24 Scale
Slightly smaller in size than the 1:12 scale, with horses roughly measuring 13cm high by 4cm wide by 15cm long. Recommended for ages 4 and up, with some of the playsets having small parts are recommended for ages 6 and up. They are geared more toward the younger horse lover, and come in many breeds, sold as a single horse or in playsets. These are affordably priced and are made with imaginative play in mind.
Horses 1:32 Scale
This scale is significantly smaller than the above with horses roughly measuring 6cm high by 3cm wide by 8cm long. They're recommended for ages 4 and up, with some of the playsets recommended for ages 6 and up. They are beautifully detailed and come in lots of breeds and colours. They come with many additonal items such as tack and barns and are featured in many lovely playsets too.
Horses 1:64 Scale
This scale model generally include the Breyer Mini Whinnie range. The size between horses of this type does not vary much in this scale, but the size of resins often vary from Breyer Mini Whinnies.