rxlist.com has this to say about the contents:
"Each 5 mL dose of ZUTRIPRO Oral Solution contains: hydrocodone bitartrate, USP, 5 mg; Chlorpheniramine maleate, USP, 4 mg; and pseudoephedrine hydrochloride, USP, 60 mg."
Keep in mind 5 mL equals about one teaspoon in terms of volume, first of all. I would watch not to take too much of this for recreation, as there is a sedating anti-histamine (chlorpheniramine) and a mild stimulant (pseudoephedrine) in addition to the hydrocodone. I don't know how much hydrocodone you usually take in tablet form, but if you can feel good from 1 single Lortab, that means you should probably try just 5 mL (one teaspoon) to see how that effects you. I would say 7.5 mL (one-and-a-half teaspoons) should be the max, not really because of the hydrocodone if you have the tolerance, but because of the two other drugs and their potential dangers combined with the hydrocodone. Even someone with a hefty opiate tolerance I would not advise to take more than 7.5 mL per dose, for the other drugs can wreak havoc at higher doses, esp. together and with the hydrocodone. I have a feeling, though, 5 mL will satisfy you if you can take one Lortab and feel good - 5 mL should have you feeling something, at the least.