This site provides a quick and easy way to do feedback divider calculations for DC-DC converters and LDOs. Pick a resistor tolerance, enter the desired output voltage, the reference voltage, the reference tolerance, and click on the "Calculate" button. The results will display in a table showing min, nominal and max output voltage, percent error, and divider current consumption. Note that the program does not account for feedback pin leakage current and finite loop gain effects.
You can optionally force the site to use a fixed upper or lower resistor value by entering the value in the input box and checking the "fixed value" box next to it. You can also optionally specify the minimum and maximum reference voltage values instead of a percent tolerance by entering the min and max values in volts in the input box seperated by a comma.
After displaying the results, the decade up and down buttons allow scaling of the resistor values to minimize divider current or to meet other system goals.
Always manually check the calculations, there is alway the possibility of bugs in the software.