pH Calculator
This pH calculator finds the pH of a solution from its hydrogen ion concentration, or works backward from a pH to the concentration. Pick what you know, type the value, and you'll get the pH, the pOH, both ion concentrations, and whether it's acidic, neutral, or basic. Everything updates as you type, so it's quick for class or the lab. It's free and runs in your browser, so nothing you enter leaves your device.
- pH and pOH
- Both ion concentrations
- Acidic or basic
- Either direction
- pH scale chart
Last updated June 17, 2026 pH = minus log H+ Reviewed by the Calcowa team
Enter a hydrogen ion concentration above zero, or a pH value.
Enter the hydrogen ion concentration in moles per liter, like 0.001 or 1e-3. The pOH and hydroxide assume water at 25 degrees Celsius, so you don't have to find the pOH yourself, since it's just 14 minus the pH.
How do you calculate pH?
pH measures how acidic or basic a solution is, and it's the negative base-10 logarithm of the hydrogen ion concentration. In plain terms, pH equals minus log of the H plus concentration in moles per liter. So if a solution has a concentration of 0.001 moles per liter, which is 1 times 10 to the minus 3, the log is minus 3 and the pH is 3, an acid. To run it the other way, you raise 10 to the negative pH, so a pH of 3 gives back 0.001. The scale usually sits between 0 and 14, with 7 neutral, lower numbers acidic, and higher numbers basic. Each whole step is a tenfold change, so a pH of 4 holds ten times the hydrogen ions of a pH of 5. Water also ties pH to pOH, the same idea built on the hydroxide concentration, and at room temperature the two always add to 14. That means one measurement gives you everything: pH, pOH, and both ion concentrations. This tool runs the logarithm or the power for you, so you'll have the answer instantly and you don't need a log table, and it fills in the partner values and labels the solution the moment you type a number. That's the whole pH scale in one tap.
Working out pH, step by step
Here's the routine for a 0.001 mol/L solution, and it's just three steps:
- 1
Pick what you knowYou have the concentration, so choose that mode.
- 2
Take the logMinus log of 0.001 is 3, so the pH is 3, an acid.
- 3
Read the partnerspOH is 14 minus 3, which is 11, and [OH-] is 1e-11.
The pH scale
Here's where everyday liquids land on the scale. You'll see how far apart an acid and a base sit, with neutral water right in the middle, and that's the dividing line.
| pH | Example | Type |
|---|---|---|
| 2 | Lemon juice | Acidic |
| 5 | Black coffee | Acidic |
| 7 | Pure water | Neutral |
| 8 | Baking soda | Basic |
| 13 | Bleach | Basic |
Frequently asked questions
You choose what you know, then type one value and it fills in the rest. From a hydrogen ion concentration it takes the negative base-10 logarithm for the pH, and from a pH it raises 10 to the negative pH for the concentration. It also works out the pOH and the hydroxide concentration, since they're linked, and labels the solution acidic, neutral, or basic. Everything runs in your browser, so nothing you enter leaves your device.
pH is the negative base-10 logarithm of the hydrogen ion concentration, written pH equals minus log of the H plus concentration in moles per liter. So a concentration of 0.001, which is 1 times 10 to the minus 3, gives a pH of 3. To go backward, the concentration is 10 to the negative pH. Because pH and pOH always add to 14 in water at room temperature, once you have one you have all four values.
The pH scale runs from 0 to 14 and measures how acidic or basic a water-based solution is. A pH of 7 is neutral, like pure water. Below 7 is acidic, and the lower it goes the stronger the acid, so lemon juice sits near 2. Above 7 is basic, also called alkaline, with bleach up near 13. Each whole step is a tenfold change in hydrogen ion concentration, so a pH of 4 is ten times as acidic as a pH of 5.
pOH is the partner of pH, the negative logarithm of the hydroxide ion concentration instead of the hydrogen one. In water at 25 degrees Celsius, pH and pOH always add up to 14, so a solution with a pH of 3 has a pOH of 11. It's handy when a problem gives you the hydroxide concentration of a base, since you can find pOH first and then subtract from 14 for the pH. This tool shows both at once.
Because the scale is logarithmic, not linear. The pH is built on a base-10 logarithm, so dropping the pH by one whole number multiplies the hydrogen ion concentration by ten. That's why a pH of 3 is ten times as acidic as 4 and a hundred times as acidic as 5. It lets a single small number describe concentrations that span many orders of magnitude, which is exactly why chemists find the scale so useful.
Yes, it's completely free, with no sign-up, and it runs right in your browser, so nothing you enter leaves your device. Pick whether you know the concentration or the pH, type it in, and read the pH, pOH, and both ion concentrations in a tap. Bookmark it for chemistry class, lab reports, or checking a buffer, and you'll have the pH formula and a worked result whenever you need them.
Related tools
More chemistry and math tools.
Molarity, dilution, pH, and more.
Molarity CalculatorMoles per liter of a solution.
Dilution CalculatorC1V1 = C2V2 made easy.
Studying acids and bases?
Find the pH above, or work out the molarity of a solution.