I have what might be a stupid question:

I was married recently and am trying to update my W4, but I'm a bit unclear about the Two Earners worksheet on page 2. Am I supposed to use Table 1 and Table 2 with GROSS wages in mind or Taxable income? My wife and I contribute quite alot to our 401ks and so our withholding's amount varies greatly on whether this worksheet is meant for total wages or not.

I haven't had much luck finding an answer online.