Mass Percent Dilution Calculator
Diluting a solution by adding solvent keeps the mass of dissolved solute fixed while raising the total mass, so the concentration falls. Using the conservation relation C1 times m1 equals C2 times m2, this calculator finds the final solution mass needed to reach your target mass percent, and the mass of solvent you must add to get there. Enter the starting concentration and mass plus the target concentration. The calculation is a pure mass balance with no empirical constant.
Mass percent dilution formula
Solute mass = (C1 / 100) * m1
Conservation: C1 * m1 = C2 * m2
m2 = (C1 * m1) / C2
Solvent to add = m2 - m1
Diluting 100 g of a 30 percent solution to 10 percent requires a final mass of 300 g, so 200 g of solvent must be added while the 30 g of solute stays constant.
Dilution facts
- The solute mass is conserved during dilution; only the solvent changes.
- Mass percent is solute mass divided by total solution mass, times 100.
- The relation needs no density and applies to any solute and solvent.
- A negative solvent-to-add value means you must remove solvent to concentrate.
- For volume-based molar dilution, use C1 times V1 equals C2 times V2 instead.
Mass percent dilution: frequently asked questions
How does mass percent dilution work?
When you dilute a solution by adding solvent, the mass of dissolved solute stays constant; only the total mass increases. Because mass percent times total mass equals solute mass, the relationship C1 times m1 equals C2 times m2 lets you find the final mass needed to reach a target concentration.
What is mass percent?
Mass percent is the mass of solute divided by the total mass of solution, multiplied by 100. A 10 percent salt solution contains 10 grams of salt in every 100 grams of solution. Enter percentages directly, for example 10 for 10 percent.
How much solvent do I add?
The solvent to add equals the final solution mass minus the initial solution mass. The calculator computes the required final mass from the conservation relation and then subtracts your starting mass to give the mass of solvent (usually water) to add.
Can I concentrate instead of dilute?
The conservation relation works whenever solute mass is conserved. If the target concentration is higher than the starting one, the required final mass is smaller and the solvent to add is negative, indicating you would need to remove solvent (for example by evaporation) rather than add it.
Does this assume any density or specific solute?
No. The mass percent dilution relation is purely a mass balance and uses no density or empirical constant. It holds for any solute and solvent as long as no solute is added or removed during dilution.
Official sources
- NIST: NIST SI units and measurement.
- IUPAC: IUPAC Gold Book: mass fraction.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.