The equivalent dose of sildenafil is five times that of tadalafil. The maximum single as-needed dose of branded Viagra is 100 mg, while the maximum dose of Cialis is 20 mg. Your current dose of tadalafil is .2 x 30 = 6 mg, which is 6 / 20 = 30% of the maximum dose. 30% of the sildenafil maximum dose would be 30 mg, which would be 1.2 ml of the 25mg/ml liquid. Note that a full dose of their liquid sildenafil would be 4 ml.
This illustrates why liquid tadalafil is a much better bargain than liquid sildenafil. The entire bottle of tadalafil contains 30 x 30 = 900 mg of product, which is 900 / 20 = 45 maximum doses, but the entire bottle of sildenafil, at the same price, contains 25 x 30 = 750 mg of product, which is 7.5 doses. So dealing at the full dose level, sildenafil is 6 times more expensive than tadalafil.
All of the above is for occasional as-needed use. Cialis is also approved for continuous daily use at a maximum dose of 5 mg per day. So if you are taking it every day, your 6 mg current dose is actually a pretty high dose, not a tiny one. But if you get a full weekend out of one 6 mg dose of tadalafil, then you are indeed a lucky man.
And all of the above also assumes that the PP products are as effective per milligram as the brand name stuff, which I personally think is doubtful.
Don’t know about Revatio.