Inherited IRA's will be taxed at your ordinary income tax rate when the money is taken out.
This will depend on the other income on your return and also the state you live in for the State income taxes.
Based on the way you asked the question, I assume you are asking this about the future, so 2018 and beyond. I have put in a link below for the 2018 tax rates, so this may help you get very close to what amount is needed to be taken out for taxes.
Many custodians of the IRA accounts will take out 20% Federal and 5% on the state (if you have state income tax) as a ballpark number. Your actual rate however may be higher or lower and the tax rate schedule can help get you closer to the actual amount.