There is a test and there is a calculator. See discussion here:
There's been a lot discussion recently in
Excelmale on wanting to test for Free E2 and the relatively high cost of this test. There are online calculators which calculate an estimate of Free T based on Total T, SHBG and Albumin. However there doesn't appear to be an online...
www.excelmale.com
The calculated values seem to line up pretty well with the tests for some guys. You do need to measure testosterone and SHBG in addition to estradiol. Ideally albumin too. The calculation seems to work better with the standard estradiol test. But this probably requires that you don't have elevated CRP to throw off the test.