How much storage space do I need to restore iPhone 5?

I've tried to restore my iPhone but it keeps saying I don't have enough storage space.
So how much (at least) storage space do I need?

The Command Module had two DSKYs connected to its AGC: one located on the main instrument panel and a second located in the lower equipment bay near a sextant used for aligning the inertial guidance platform. The Lunar Module had a single DSKY for its AGC. A flight director attitude indicator (FDAI), controlled by the AGC, was located above the DSKY on the commander's console and on the LM.