About Dilution Calculator
Diluting a solution doesn't change how much solute is in it — it only spreads the same amount across more volume, which is exactly what C1V1 = C2V2 says: concentration times volume (the total amount of solute) before dilution equals concentration times volume after, because that quantity didn't go anywhere.
Four numbers are involved and any three pin down the fourth, but in practice the question is almost always the same one: 'I have a stock solution at C1, I want a target concentration C2 in a final volume V2 — how much stock (V1) do I actually measure out?' That's the calculation this defaults to, though every other rearrangement works the same way.
The instruction that trips people up: once V1 is known, the rest of the final volume is made up with solvent — but 'add V2 of solvent' is wrong and overshoots the target, because V1 is already part of V2. The correct instruction is to add solvent until the total volume reaches V2, which is a smaller amount of solvent than V2 itself by exactly V1.
How to use the dilution calculator
Enter three of the four values
Stock concentration, stock volume, target concentration, final volume.
Read the fourth
Calculated directly from the other three.
Make it up correctly
Add solvent until the total reaches the final volume — not by adding that much solvent on top.