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How to Remember Prefixes for SI Units of Measure

Prefixes according to the International System of Units are often used in scientific vernacular as a way of determining the scale of metric values. For example, it's important to know if you're dealing with megabytes of data or petabytes of data. The difference between the two is 1,000,000-fold. It's a good idea to keep the prefixes for measured units in your mind and one easy way of doing this is remembering them based on mnemonic devices.

Instructions

- 1
  Read the list of prefixes and commit them to memory. You might have trouble remembering each one or the order in which they go, but a mnemonic device can help you recall this information. The list of prefixes is as follows: exa-, peta-, tera-, giga-, mega-, kilo-, base unit (ones), milli-, micro-, nano-, pico-, femto-, atto-.
- 2
  Picture the scene of speakers killing very small flowers that were picked by lawyers. The scene should bring to mind the phrase: "Exacting Petals, Terribly Gigantic Megaphones Killed 1 Million Microscopic Nasturtiums Picked Freshly by Attorneys." The first letter of each word in the phrase should help you recall the first letter in the corresponding prefix list. This is especially useful if you get confused about the order of prefixes; for example, is atto- or femto- the larger prefix?
- 3
  Recall the prefix and apply it to the unit of measure you're working with. For example, if you're working in grams and measuring amounts in fractions of a gram that approximate the thousandths range, you should refer to your measurements in "milligrams."
- 4
  Remember the units of hecto-, deka-, deci- and centi- by memorizing the phrase "Kings Have Diamonds But Diamonds Cost Money." These prefixes, however, are not commonly used in scientific references, aside from "deci-" when referring to "decibels" and "centi-," which is easy to remember because centimeters are common length measurement units.

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