I often find I have too much information to remember (and for some reason people expect me to be able to spout pixel aspect ratio numbers like a multiplication table). Fortunately the fine folks over at Digital Rebellion has solved this (and for free). They offer several video widgets that do important math, these run on a web browser or iPhone (and a couple can run offline as well).
Video Footage Calculator – Calculates how much storage you'll need for your footage type and duration.
Web – iPhone version – Offline version
Film Rate Calculator – Determines how much film you need for a particular scenario.
Web – iPhone version – Offline version
Aspect Ratio Calculator – Determines the aspect ratio for different footage formats.
Web – iPhone version
Depth of Field Calculator – Calculates depth of field for many camera sensors.
Web – iPhone version
Pixel Aspect Ratio Calculator – Determines relationship of Pixels for many digital formats.
Web – iPhone version
Lens Angle Calculator – Helps calculate the lens angle for a given sensor size and focal length.
Web – iPhone version
Power Load Calculator – Calculates the load on a circuit to see if it is excessive. You can also calculate the minimum circuit breaker size for the given load.
Web – iPhone version
These tools are cool, free, and useful.... three points that make them a must have for my iPhone.