The base quantities used in the SI are length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. The base quantities are by convention assumed to be independent. The corresponding base units of the SI were chosen by the CGPM to be the metre, the kilogram, the second, the ampere, the kelvin, the mole, and the candela. The derived units of the SI are then formed as products of powers of the base units, according to the algebraic relations that define the corresponding derived quantities in terms of the base quantities. When the product of powers includes no numerical factor other than one, the derived units are called coherent derived units.

The name Système International d'Unités, (International System of Units) and the abbreviation SI, were established by the 11th General Conference on Weights and Measures (CGPM) in 1960.

Symbols for quantities are generally single letters set in an italic font, although they may be qualified by further information in subscripts or superscripts or in brackets. Note that symbols for quantities are only recommendations, in contrast to symbols for units whose style and form is mandatory.

Insert or select compound name (e.g. triglycerides) in the first field and value in the left hand field of the second or third section. Then click "yield" button for conversion into the wanted unit. Notice units indicated in the table (JAVA script must be activated).

By this point, you will have hopefully learned how to quickly and easily convert between the various SI unit prefixes. If not, remember that practice makes perfect. Keep trying, and soon it will seem simple. Remember two key points: It is beneficial to memorize the table of prefixes, and the best way to approach the problems is to ask, “How many of the first unit are in one of the second unit?” You can use that information to set up a dimensional analysis problem that will get you to your answer quickly.

Another way to approach these problems is to ask, “How many kilograms fit inside 1 megagram?” To answer this, look at the meaning of the two units: 1 kilogram is 103 grams, while 1 megagram is 106 grams. If we divide megagrams by kilograms, we see that there are 1000 kilograms in 1 megagram. So, we can set up a different factor to solve the conversion:

These reference tables show the different bases and prefixes used to designate metric units with the SI system.

Units of measurement as defined by metrology, the scientific study of measurement. ADDucation’s units of measurement list includes Metric SI units (International System of Units), Imperial units and United States Customary System (USCS). Where British, American, Canadian and Australian imperial units of volume differ we’ve included the differences.

Converting between the different SI system prefixes is an essential science skill that requires practice. Memorizing the different prefixes and their meanings makes it a lot easier to do these conversions, so try to memorize as many as you can. Of course, you can always refer back to the tables above.

Femto is equivalent to 10-15, and milli, as noted in the problem above, is equivalent to 10-3. Thus, since we are going up the table, the difference here is 10-12.

These base units can be combined with any of the prefixes to create units that are most appropriate for what is being measured. For example, you wouldn’t measure the distance from LA to New York in meters, the base unit. Instead, you would use kilometers, or even megameters. The different base units can also be combined to form what are called derived units. For example, speed can be measured in meters per second, or in kilometers per nanosecond. The combinations are endless.

This problem brings up a particularly interesting property of SI unit conversions. As we look at the table of conversions, notice that all the conversion factors are in scientific notation. That is, they are in the form 10x. So, yet another way to solve these problems is to just consider how many places the decimal point has to move over to successfully complete the conversion. 7.98 x 10-8 is the same as 0.796 x 10-9, just with an adjustment to comply with standard scientific notation. Also notice that nanograms refers to 10-9. So, for the following problems, the solution will be given using this shortcut method.

[t]he bronze yard No. 11, which was an exact copy of the British imperial yard both in form and material, had shown changes when compared with the imperial yard in 1876 and 1888 which could not reasonably be said to be entirely due to changes in No. 11. Suspicion as to the constancy of the length of the British standard was therefore aroused.

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Here is an example of a one-step conversion between the SI system prefixes. Let’s try converting 955 kilograms to megagrams. We will need two pieces of information from the table above. Kilogram refers to 103 grams, while megagram refers to 106 grams. Using these two pieces of information, we can set up a dimensional analysis conversion.