How the object size in R are calculated?

Question

> print(object.size(runif(1e6)),unit="Mb")
7.6 Mb

This gives me 7.6Mb for a vector with 1 million elements. But why? each element is 32 bit or 64 bit? I cannot add these numbers up.

Answer 1

They're 64-bit (8-byte) floating point values. One megabyte (Mb) is 2^20 bytes (not 10^6 - see below) ... so ...

8*1e6/(2^20)
[1] 7.629395

Lots of potential for confusion about what Mb means:

• according to Wikipedia "MB" is the recommended abbreviation for "megabyte", but R uses "Mb"
• there is plenty of confusion about whether "mega" means 10^6 or 2^20 in this context.

As usual, this is clearly documented, deep in the details of ?object.size ...

As illustrated by below tables, the legacy and IEC standards use binary units (multiples of 1024), whereas the SI standard uses decimal units (multiples of 1000) ...

 *object size* *legacy* *IEC* \n   1 1 bytes 1 B   \n1024 1 Kb 1 KiB \n1024^2 1 Mb 1 MiB \n

Google's conversion appears to use SI units (1 MB = 10^6 bytes) instead.