when an ARF is described as .40, .60 or 1.50, what exactly does that mean or refer to?

how do they correspond to various "scales" (i.e. 1/5, 1/6, etc.) that I see many references to?

thanks for the info,

the .40, .60 etc corresponds to the engine displacement that the kit is built around, ie needed to fly it. dick

A 1/6th scale P51 might require a .46 cu in size engine whereas a 1/6 scale Piper Cub might require an .15 cu in. Usually a kit will have both designations as well as wingspan, length, wing area and wing loading. After you have been in the hobby for a while all you need is a couple of those pieces of information and if you are familliar with the airplane style you can guess at the rest pretty well.

Right. There's no direct correlation between .40, .60, 1.20 (engine size) and scale.
Dennis-

in general, and this is really stretching it at best, .40 is about 15% scale, and 1.20 is usually about quarter scale. that said, there isn't much correlation and it depends on the plane more than anything else. (a 1.20 scale bomber isn't exactly 25%!!)