1m to 39m (depending on the algorithm)
Sets the apparent size (roughly equal to the longest dimension in meters) and how fast the diffusion builds up.
It also affects the Reverb Time Mid (RTM), Spread (SPR), and modulation engine.
The Size control changes the density of the reverb. If you set it to a higher number, the sound will be smaller and more dense. If you set it to a lower number, the sound will be bigger and less dense.
The overall sense of size is a combination of the parameters Size, Shape, and Spread.