You can measure water by weight too. 4.26 oz (weight) = 4.26 oz (volume)
Only at 4°C, and only if we're talking about avoirdupois fluid ounces. At 20°C one US customary fluid ounce of water has a mass of 1.041 avoirdupois ounces.
Anyway, the problem with solutions is that mass/volume don't usually scale linearly with concentration. If it's important to get a precise result, you'll need to look up a table for that particular solute/solvent.