The golang specification says, "float64 is the set of all IEEE-754 64-bit floating-point numbers." which is commonly known as double precision numbers,
http://en.wikipedia.org/wiki/Double-precision_floating-point_format
You can read all of its glory details if interested, but to answer your question, quote,
"...next range, from 253 to 254, everything is multiplied by 2..."
So if you want to use it as counters, i.e. positive integers, you won't have problem until 253=9,007,199,254,740,992.