Dilution calculator
Leave any one of the four boxes empty and this fills it in, along with how much solvent you actually have to add. It is the easiest formula in chemistry, and that is exactly what makes it a bad teacher. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
The units cancel, and that is the problem
C₁V₁ = C₂V₂ rearranges to V₁ = C₂V₂ / C₁. Both concentrations appear once on each side of the division, so whatever unit they are in disappears. The same is true of the volumes.
That means the formula works in any units, as long as each pair matches. Which sounds like a feature, and is, until you notice what it teaches: somebody who learns dilution through this formula never once has to think about units, because the formula never punishes them for not thinking about units.
Then they meet C₁ in mol/L and C₂ in g/L, and the arithmetic produces a number with total confidence. Nothing here can catch that. It is the same trap Boyle's law sets, for the same reason, and it is worth naming rather than enjoying.
The answer you want is usually the solvent
Solving for V₁ tells you how much stock to measure out. It does not tell you how much water to add, which is the thing you actually do at the bench — and that is V₂ − V₁, shown above with the rest.
Add the solvent to the stock until you reach the final volume, rather than measuring out the difference and adding it. The two are not quite the same for concentrated solutions, for the same reason a litre of water plus a mole of salt is more than a litre.
A note on the atomic weight table
This page does not use atomic weights — it works in whatever units you give it. It does load the site's table, because it shares a library with the molar mass tools, so the acknowledgement belongs here as well: the table is the abridged standard atomic weights 2024, © IUPAC / CIAAW, published at ciaaw.org and reproduced under their terms.