Find [H⁺] from pH 7
Input
pH = 7.00
Output
pH = 7.00, pOH = 7.00, [H⁺] = 1.00 × 10^-7 mol/L, [OH⁻] = 1.00 × 10^-7 mol/L
pH Calculator (pH, pOH, and concentration conversion)
A simple pH calculator to convert H+, pH, and pOH for education and quick field notes. It helps you check pH calculation, pOH calculation, and hydrogen ion concentration in one place.
Three input tabs so the starting point is obvious
pH / pOH / [H⁺] / [OH⁻] shown as one fixed set
Formula view, copy, and share URL included
Temperature and activity cautions kept visible
Calculation assumptions
This tool performs a basic conversion from concentration to pH and does not handle activity.
The ion product of water (pKw) and the neutral point vary with temperature, but this tool uses the basic value pKw = 14.00.
Errors can become larger for concentrated solutions, buffered systems, or solutions with high ionic strength.
How to use
- Choose whether you want to start from pH, [H⁺], or pOH.
- Enter a value to calculate pH / pOH / [H⁺] / [OH⁻] immediately.
- Add a temperature note if needed, and adjust significant figures for concentration output.
- Turn on Show formulas when you want to see the equation and substitution steps.
- Copy the result or share the current setup by URL.
Common examples
Find pH from [H⁺] = 1 × 10^-3
Input
[H⁺] = 1e-3 mol/L
Output
pH = 3.00, pOH = 11.00
Check the basic side from pOH 5
Input
pOH = 5.00
Output
pH = 9.00, [OH⁻] = 1.00 × 10^-5 mol/L
Calculation assumptions
- This tool performs a basic conversion from concentration to pH and does not handle activity.
- The ion product of water (pKw) and the neutral point vary with temperature, but this tool uses the basic value pKw = 14.00.
- Errors can become larger for concentrated solutions, buffered systems, or solutions with high ionic strength.
Glossary
pH
A logarithmic expression of hydrogen ion concentration.
pOH
A logarithmic expression of hydroxide ion concentration.
pKw
The logarithmic form of the ion product of water. Around 25°C, 14 is often used as the basic value.
Activity
An effective concentration term used to describe non-ideal behavior, especially in concentrated or high-ionic-strength systems.
Buffer solution
A system that resists pH change when acid or base is added, so it cannot be handled by simple pH-to-concentration conversion alone.
Formulas
pH = -log10([H+])pOH = -log10([OH-])pH + pOH = 14.00[H+] = 10^(-pH)[OH-] = 10^(-pOH)
Frequently asked questions
Does temperature change the result?
Strictly speaking, yes. This tool uses the basic assumption pKw = 14.00 and treats temperature as a note only.
Can I use this for buffers?
Not directly. Buffer systems need a different model, so a simple pH-to-concentration conversion is not enough.
Is this enough for research work?
Treat it as an estimate. For research or quality control, use actual measurements, calibration standards, and activity-aware methods when needed.
What unit does [H⁺] use here?
This tool assumes mol/L (M).
Is pH + pOH always 14?
Fourteen is a common basic value near 25°C, but pKw changes with temperature. This tool fixes it at 14.00 for basic calculations.
Important notes
- This tool is intended for education and quick field notes.
- Actual measurements can differ because of temperature, activity, and ionic strength.
- For research or quality control, use a calibrated pH meter and the appropriate corrections for your conditions.
- Do not rely on this basic calculation alone for buffers or highly concentrated systems.