Water Needed to Dilute

Diluting does not change the amount of solute, so the final mass grows by the ratio of the starting concentration to the target.

Your numbers

Concentration(%)Solution (g)(g)Target %(%)

Water to add

900g

Solution (g)

1,200g

Formula

Water to add = Solution (g) × (Concentration ÷ Target % − 1)

Taking 300 g of 20% down to 5% needs 900 g more water for 1,200 g total — quartering the strength quadruples the volume.

What to enter

Input	Default	Accepted range
Concentration (%)How much of the whole is solute.	20	0.01 ~ 100
Solution (g) (g)Solute and solvent together.	300	0 and up
Target % (%)The concentration you want; lower means add water, higher means add solute.	5	0.01 ~ 100

Step by step

FormulaWater to add = Solution (g) × (Concentration ÷ Target % − 1)

With the default numbersWater to add = 300 × (20 ÷ 5 − 1)

AnswerWater to add = 900 g

Quick reference table

Results when only Concentration (%) changes and everything else stays put.

Concentration (%)	Water to add (g)	Solution (g) (g)
10	300	600
15	600	900
20	900	1,200
30	1,500	1,800
40	2,100	2,400

What each result means

Result	At default values
Water to add (g)Extra water needed to reach the target.	900
Solution (g) (g)Solute and solvent together.	1,200

Common mistakes

Taking 300 g of 20% down to 5% needs 900 g more water for 1,200 g total — quartering the strength quadruples the volume.

Glossary

Concentration: How much of the whole is solute.
Solution (g): Solute and solvent together.
Target %: The concentration you want; lower means add water, higher means add solute.
Water to add: Extra water needed to reach the target.

Frequently asked questions

QHow is Water Needed to Dilute calculated?

Water to add = Solution (g) × (Concentration ÷ Target % − 1) — Diluting does not change the amount of solute, so the final mass grows by the ratio of the starting concentration to the target.

QCan you walk through an example?

With Concentration 20%, Solution (g) 300g, Target % 5%, the answer is Water to add 900g.

QWhat do I need to enter?

Enter Concentration, Solution (g), Target %. The result recalculates as you type, and an empty box counts as zero.

QHow much does the answer move if I change a number?

Changing only Concentration (%) moves the answer to Concentration (%) 10 → Water to add (g) 300 and Concentration (%) 40 → Water to add (g) 2,100. The table below lays out five steps.

QHow are the numbers rounded?

Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.

QAnything to watch out for?

Taking 300 g of 20% down to 5% needs 900 g more water for 1,200 g total — quartering the strength quadruples the volume.

Related calculators

Concentration CalculatorGet percent concentration from the mass of solute and solution.Mixing Two SolutionsFind the resulting concentration when two solutions of different strengths are combined.Make a Saline SolutionWork out the mix needed to make a given amount at a target concentration.Fold Dilution CalculatorConvert a dilution like "1:1000" into the millilitres of stock you need.

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