pH Calculator
Calculate pH values for science, physics, chemistry, and engineering problems.
This pH calculator converts between hydrogen ion concentration [H+] and pH, the standard logarithmic scale used to describe how acidic or basic (alkaline) a solution is.
Enter either the hydrogen ion concentration or the pH value, and the calculator returns the other.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| [H⁺] = 1 × 10⁻⁴ M | pH = 4 | pH = −log₁₀(1×10⁻⁴) = 4 - a moderately acidic solution. |
| pH = 8.5, find [H⁺] | [H⁺] ≈ 3.16 × 10⁻⁹ M | [H⁺] = 10⁻ᵖᴴ = 10⁻⁸·⁵ ≈ 3.16 × 10⁻⁹ M - a mildly basic solution. |
The pH Formula
pH = -log10[H+], where [H+] is the hydrogen ion concentration in moles per liter. Because pH is a logarithmic (base-10) scale, each whole-number decrease in pH represents a tenfold increase in hydrogen ion concentration - a solution with pH 4 is ten times more acidic than one with pH 5.
The pH Scale: Acidic, Neutral, and Basic
The pH scale typically runs from 0 to 14. A pH of 7 is neutral (pure water). Values below 7 are acidic (higher hydrogen ion concentration), and values above 7 are basic or alkaline (lower hydrogen ion concentration) - though pH values outside 0-14 are possible for very concentrated solutions.
How to Use the pH Calculator
- Open the pH Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the ph calculator works.
Frequently Asked Questions
How do you calculate pH?
pH = -log10[H+], where [H+] is the hydrogen ion concentration of the solution in moles per liter.
What does a pH of 7 mean?
A pH of 7 is neutral, meaning the concentration of hydrogen ions and hydroxide ions are equal - pure water at 25°C has a pH of 7.
Why is pH measured on a logarithmic scale?
Hydrogen ion concentrations vary across an enormous range in real solutions, so a logarithmic scale compresses that range into manageable numbers - each one-unit change in pH represents a tenfold change in hydrogen ion concentration.
How do I use this ph calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the pH Calculator calculate?
Calculate pH values for science, physics, chemistry, and engineering problems. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this ph use?
The formula is: pH = −log₁₀[H⁺]. The pH scale was introduced by Danish chemist Søren Sørensen in 1909 while working at the Carlsberg Laboratory studying the chemistry of beer brewing, of all things - he needed a convenient way to express the very small hydrogen ion concentrations relevant to fermentation without writing out unwieldy decimal fractions. The 'p' in pH is generally understood to stand for 'power' or the German 'potenz,' reflecting the logarithmic, power-of-ten nature of the scale.
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Last updated: September 27, 2026.