Ford Taurus 2004 o2 sensors

What length o2 sensors ( upstream and downstream) do I need for Ford Taurus 2004

The upstream O2 sensor should fluctuate from 0.1 to 0.9 volts. The downstream O2 sensor should be steady at 0.45 volts normally but anything over 0.1V or under 0.9V is ideal as long as it is a steady reading.

Visit a Ford dealer and get the right part.

After reading your question my advice is to quit trying to play mechanic!
You don't measure the length of an 02 sensor. If you get 02 sensor codes you identify the location the code refers too and then either take a chance buying direct fit after market 02 sensors or you take your VIN to the dealer to make sure you get the correct 02 sensor.
I'd be monitoring an 02 sensors electrical readings before just tossing an 02 at the vehicle to make sure it is actually bad!

Hi do the sensible thing take it to someone who knows.