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Yup. You can safely assume a float is 4 bytes everywhere. 
boolean = 1 byte (not 1 bit!)
byte = 1 byte
short = 2 bytes
int = 4 bytes
long = 8 bytes
float = 4 bytes
double = 8 bytes
char = 2 bytes
reference = 4 or 8 bytes (in most cases 4 bytes, even on 64-bit systems)