Free tools for server admins

Small calculators and generators that answer one question each, run entirely in your browser, and ask for nothing. Nothing you type is sent anywhere unless you choose to email yourself the result.

RAID calculator
Usable capacity, fault tolerance and speed for RAID 0, 1, 5, 6, 10, 50 and 60 — in the decimal TB disks are sold in and the TiB your operating system reports.
Bandwidth calculator
Turn visitors and page weight into the monthly data transfer a hosting plan has to include — and the sustained megabits per second that works out to.