Use the conversion chart determined by psychologists Frey and Detterman. It is listed first under References and is valid if you took the SAT before 1996. If you took the SAT after 1996 but before 2004, use their formula: IQ =(0.095 x SAT math) + (0.003 x SAT verbal) + 50.241. If you took the test after 2004, Detterman says, this formula should still work, although it has not been updated.
Look at Mensa society member Rodrigo de la Jara's IQ Comparison website, which includes a table that correlates SAT scores to IQ. If you scored 1010 on the SAT, for example, you have an estimated IQ of 110. If you scored 1530, your estimated IQ is 147.
Check the Braingle website's SAT score converter or the chart at Assessment Psychology Online to see how they correlate your SAT score to the IQ scale.