I dont think you can convert them because of the value differences
contained in each vitamin, altho they mention some conversions in this
explanation below from: http://www.unc.edu/~rowlett/units/dictI.html

*International Unit (IU)*

"A unit used to measure the activity (that is, the effect) of many
vitamins and drugs. For each substance to which this unit applies,
there is an international agreement specifying the biological effect
expected with a dose of 1 IU. Other quantities of the substance are
then expressed as multiples of this standard. Examples: 1 IU represents
45.5 micrograms of a standard preparation of insulin or 0.6 microgram
of a standard preparation of penicillin. Consumers most often see IU's
on the labels of vitamin packages: in standard preparations the
equivalent of 1 IU is 0.3 microgram (0.0003 mg) for vitamin A, 50
micrograms (0.05 mg) for vitamin C, 25 nanograms (0.000 025 mg) for
vitamin D, and 2/3 milligram for (natural) vitamin E. Please note: for
many substances there is no definite conversion between international
units and mass units (such as milligrams). This is because preparations
of those substances vary in activity, so that the effect per milligram
of one preparation is different from that of another."

Most vitamins are based on the IU values, so why do you want to convert
them when you do not buy them that way?
http://www.changingshape.com/resources/references/vmchart.asp

To do some further research on your vitamin choices, this is a good
website for more details on how much is too much etc:
http://tinyurl.com/5f2e7

<<joni>>

Why would you?  The IU's are the important things to know when figuring out
if you're getting your DRI or getting too much so that the vitamin works as
a pro-oxidant instead of an anti-oxidant and is possibly becoming toxic.