Lightmap size

lets say i have a cube with 1024 resolution lightmap. so what is the cost ( disk size ) for this uncompressed lightmap texture. is it same as compressed mip textures?

lightmaps get combined, i think its either in project or world settings where you can change that.
Normally all lightmaps get combined to 2k/2k atlasses.

You could probably consider them close to dxt1, but when uncompressed they are much bigger in filesize. up to four times if I am correct.