Question: how to tell how many gb my iphone is without turning it on?
Answer: STEP 1: Browse to SETTINGS > GENERAL > ABOUT.
STEP 2: Scroll down to CAPACITY.
STEP 1: Browse to SETTINGS > GENERAL > [DEVICE] STORAGE.
STEP 2: Look toward the top right to find the available and total capacity (for example, 56 GB of 512 GB Used)