Is 1 oz the same as 1 fl oz?

To put it simply: No, fluid ounces are not the name same as ounces.

Is 8 fl oz the same as 8 oz?

Water (and similar liquids that are mostly water like milk and strained fruit juices) has the exact same volume measure as weight: 8 fluid ounces (volume) of water weighs 8 ounces.

Is 3.4 oz the same as 3.4 fl oz?

A: Nothing. They are the same. Fl stands for fluid. Oz stands for ounces.

Is 1 oz liquid the same as 1 oz weight?

Most of the confusion regarding weight and volume measurements occurs when talking about ounces: an imperial unit of measurement which can be used to indicate both weight AND volume. Fluid ounces refers to volume (like milliliters) whereas regular ounces refer to weight (like grams).