Dilution Calculator
This dilution calculator solves the C1V1 equals C2V2 equation for whatever you're missing. Pick the value to find, enter the other three, and you'll get the answer, and when you solve for the stock volume it shows how much water to add. Everything updates as you type, so it's quick for lab prep or homework. It's free and runs in your browser, so nothing you enter leaves your device.
- C1V1 = C2V2
- Stock to draw
- Water to add
- Any unit
- mL or L
Last updated June 17, 2026 C1V1 = C2V2 Reviewed by the Calcowa team
Enter the three known values above zero.
Concentrations use any unit, like M, percent, or mg/mL, as long as C1 and C2 match. The dilution factor is how many times the stock is weakened. Water to add shows only when solving for V1.
How do you calculate a dilution?
Diluting a solution means adding solvent, usually water, to lower the concentration, and the whole thing rests on one tidy equation: C1V1 equals C2V2. The C1 and V1 are the concentration and volume of your concentrated stock, and C2 and V2 are what you want once it's diluted. It works because diluting doesn't change how much solute you have, only how spread out it is, so the amount on each side has to match. The most common question is how much stock to draw, which you get by rearranging to V1 equals C2 times V2 divided by C1. Picture a 10 molar stock and a goal of 100 milliliters at 1 molar: that's 1 times 100 over 10, so 10 milliliters of stock, topped up with 90 milliliters of water to reach 100. A handy feature of the formula is that the units cancel, so it works just as well with percent or milligrams per milliliter, as long as both concentrations use the same one. This tool solves for any of the four values and, when you solve for V1, tells you the water to add, so you'll know exactly what to pour the moment you type your numbers.
Diluting a stock, step by step
Here's the routine to make 100 mL of 1 M from a 10 M stock, and it's just three steps:
- 1
Pick what to solve forYou want the stock volume, V1, so choose that.
- 2
Enter the other threeC1 is 10, C2 is 1, and V2 is 100 milliliters.
- 3
Read the answerV1 is 10 milliliters of stock, so add 90 milliliters of water.
Stock and water for 100 mL
Here's how much 10 M stock and water make 100 mL at a few target concentrations. You'll see the stock shrink as the target gets weaker.
| Target (C2) | Stock (V1) | Water |
|---|---|---|
| 5 M | 50 mL | 50 mL |
| 2 M | 20 mL | 80 mL |
| 1 M | 10 mL | 90 mL |
| 0.5 M | 5 mL | 95 mL |
Frequently asked questions
You pick which value you're missing, then enter the other three from the dilution equation. It rearranges C1V1 equals C2V2 to solve for the one you left out, and when you solve for the stock volume it also tells you how much water to add. Everything runs in your browser, so you'll see the answer update as you type, and nothing you enter leaves your device. Concentrations use any matching unit, since the equation is a ratio.
It's C1V1 equals C2V2, where C1 and V1 are the concentration and volume of your starting stock, and C2 and V2 are the concentration and volume you want after dilution. The amount of solute stays the same, so its two ways of being written are equal. Rearranged, the stock volume you need is C2 times V2 divided by C1. The water you add is just the final volume minus that stock volume.
First find how much stock you need with C2 times V2 divided by C1, then subtract that from the final volume. Say you have 10 molar stock and want 100 milliliters at 1 molar: you need 1 times 100 over 10, which is 10 milliliters of stock, so you add 90 milliliters of water. The calculator shows both numbers when you solve for the stock volume, so you don't have to do the subtraction yourself.
Not as long as both concentrations use the same unit, because the equation is a ratio and the units cancel. You can work in molarity, percent, milligrams per milliliter, parts per million, or anything else, provided C1 and C2 match. The same goes for the two volumes. So a stock at 50 percent and a target at 5 percent behaves exactly like 50 molar to 5 molar in the math. Just keep each pair consistent and you're fine.
A serial dilution is a chain of step-by-step dilutions, where the diluted solution from one step becomes the stock for the next. Microbiologists use it to reach very low concentrations, like going 1 to 10 several times for a final 1 in 1,000. This tool handles one step at a time, so for a serial dilution you'd run it once per step, feeding each result in as the new starting concentration. Each step uses the same C1V1 equals C2V2.
Yes, it's completely free, with no sign-up, and it runs right in your browser, so nothing you enter leaves your device. Choose what to solve for, type the three values you know, and read the answer in a tap. Bookmark it for lab work, mixing cleaning solutions, or chemistry homework, and you'll have the C1V1 equals C2V2 formula and the water to add right where you need them.
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Prepping a solution?
Solve the dilution above, or find the molarity of a solution.