kbps means kilobits per second and KB/sec means kilobytes per second. There are 8 bits in a byte and kilo means a thousand and in computers a thousand is 1024. So if you were to multiply the KB/sec speed by 8 it should equal up to the kbps, or at least pretty close.
Internet connection speeds are almost always in bits. So you are supposed to have 3 megabits per second for downstream on you connection, it means you can transfer around 375KB per second at maximum and under ideal conditions.
When you see file sizes for things it is in bytes and not bits.