Dilute a brine by weight: use the total solution mass
Calculate added water from an existing salt solution and a lower target mass percentage without confusing water-only and solution-based ratios.
Method
First establish what the percentage describes. A mass percentage uses salt mass divided by total solution mass, multiplied by 100. A recipe that divides salt by water mass uses a different denominator. Keep all masses in the same unit. When diluting an existing solution with pure water, salt mass stays constant while total mass increases. The target must be positive and lower than the starting concentration for this dilution method.
Worked example
Suppose 500 G of solution contains 25 G of salt: 25 ÷ 500 × 100 = 5%. To reach 2%, the required total mass is 25 ÷ 0.02 = 1,250 G. Add 1,250 − 500 = 750 G of water. The check is 25 ÷ 1,250 × 100 = 2%. The original solution contained 475 G of water, so the final water mass is 1,225 G. Dividing 25 by 1,225 answers the water-based question instead of the final solution percentage.
Checks and limits
Use Brine salinity to verify salt plus water as the total solution. More generally, added water = initial solution mass × (initial percentage ÷ target percentage − 1). This assumes a well-mixed solution with no salt or liquid lost. It does not describe volume percentages or convert a volume into a mass without density. Food ingredients can introduce extra water and solutes. This is an arithmetic guide, not a preservation procedure; use a tested recipe for food storage and fermentation.
Related calculators
Source: NIST — mass units