The topic of scale within potential MP BW toys came up in a topic on TFW2005. There's no definitive scale within the show as some characters seem to grow or shrink between episodes, but using heights given by the Japanese trading cards combined with the observations from the show, we came up with the following:
http://orig05.deviantart.net/62a9/f/...0x-da2mxu0.png
Taking MP Primal as the benchmark, who is 19cm tall, if we're happy with his height in the show as 2.5m, it means that every centimeter of MP toy represents 13.15cm. Using that same scale for the rest of the Season 1 cast, we end up with the following:
Blackarachnia - 2m (15cm)
Rattrap - 2m (15cm)
Scorponok - 2.1m (16cm)
Waspinator - 2.2m (16.5cm)
Airazor - 2.3m (17.5cm)
Cheetor - 2.3m (17.5cm)
Tarantulas - 2.3m (17.5cm)
Optimus Primal - 2.5m (19cm)
Tigatron - 2.5m (19cm)
Terrorsaur - 2.5m (19cm)
Rhinox - 2.8m (21cm)
Inferno - 2.8m (21cm)
Dinobot - 2.9m (22cm)
Megatron - 3m (23cm)