pH & Concentration Calculator
Enter one known value to calculate the others. This tool assumes standard conditions at 25°C, where pH + pOH = 14 and Kw = 1.0 × 10-14.
What is a pH concentration calculator?
A pH concentration calculator helps you convert between pH, pOH, hydrogen ion concentration [H+], and hydroxide ion concentration [OH-]. In chemistry, these values are tightly connected, so if you know one, you can calculate all the others.
This is useful in chemistry class, lab preparation, water testing, biology, food science, and any process where acidity or basicity matters.
Core formulas used
- pH = −log10([H+])
- pOH = −log10([OH-])
- pH + pOH = 14 (at 25°C)
- [H+] × [OH-] = Kw = 1.0 × 10-14 (at 25°C)
Because these equations are linked, you only need one valid input to get the full acid-base picture.
How to use this calculator
Step-by-step
- Select the type of value you already know (pH, [H+], pOH, or [OH-]).
- Enter the numeric value in the input box.
- Click Calculate.
- Read the computed pH, pOH, [H+], [OH-], and the acid/base classification.
Example inputs
- pH = 2 → strongly acidic solution
- [H+] = 1e-7 mol/L → near neutral water at 25°C
- pOH = 3 → basic solution (pH = 11)
Interpreting your result
In basic terms:
- pH < 7: acidic
- pH = 7: neutral
- pH > 7: basic (alkaline)
Every 1-unit pH change corresponds to a 10× change in hydrogen ion concentration. That means pH 4 is ten times more acidic than pH 5, and one hundred times more acidic than pH 6.
Common mistakes to avoid
- Entering negative concentrations (not physically valid for [H+] or [OH-]).
- Forgetting that pH is logarithmic, not linear.
- Using the 25°C assumptions in systems with very different temperatures.
- Confusing pH with concentration units (pH is unitless; concentration is mol/L).
Quick FAQ
Can pH be less than 0 or greater than 14?
Yes, in very concentrated solutions. The common 0–14 range is a practical classroom range, but not a strict universal limit.
Why does temperature matter?
The ion-product constant of water (Kw) changes with temperature, so the pH/pOH relationship shifts. This calculator uses the standard 25°C approximation.
What unit is concentration shown in?
Molarity, written as mol/L (moles per liter).
Final note
If you need a fast way to convert pH, pOH, [H+], and [OH-], this calculator gives reliable values with minimal input. It is ideal for quick checks, homework, and lab planning under standard conditions.