pH Calculator for Acids, Bases, and Solutions
This pH Calculator converts between pH, pOH, hydrogen ion concentration [H⁺], and hydroxide ion concentration [OH⁻] in real time, and works out the pH of strong and weak acid or base solutions step by step. It is built for chemistry students checking homework and lab work where you need a fast, accurate answer.
Enter a single value in Quick Convert and the other three appear instantly on a visual 0–14 scale, or switch to Solution pH to calculate from a substance, concentration, and Ka/Kb. The math behind it is simple to state: pH + pOH = 14, [H⁺] = 10-pH, and [H⁺] × [OH⁻] = 10-14 at 25°C.
How to Use the pH Calculator
Quick Convert mode
Enter one value
Type any single value — pH, pOH, [H⁺], or [OH⁻]. You only need one to start.
Read the other three
The remaining three values are calculated automatically as you type, to four decimal places, with concentrations shown in scientific notation.
Check the scale and badge
The pH scale indicator slides to your value on the 0–14 bar, and a badge labels the solution Acidic, Neutral, or Basic with a strength description.
Try a preset
Click any of the Common Solutions presets (Lemon Juice, Pure Water, Bleach, and more) to instantly load a typical pH value.
Solution pH mode
Choose the solution type
Pick Strong Acid, Weak Acid, Strong Base, or Weak Base.
Select a substance or enter Ka/Kb
Choose a built-in substance to auto-fill its Ka or Kb, or type a custom value. For strong acids and bases, just pick the species.
Enter concentration and calculate
Type the molar concentration (M) and click Calculate to get pH, pOH, [H⁺], and [OH⁻].
Open the Solution Steps
Expand Solution Steps to follow the full working — equilibrium setup, value substitution, the quadratic for weak species, and the final pH.
Features
Quick Conversion
Enter one of pH, pOH, [H⁺], or [OH⁻] and the other three are calculated instantly to four decimal places.
Visual pH Scale
An interactive 0–14 gradient bar with a moving indicator shows exactly where your solution sits on the spectrum.
Acidic / Neutral / Basic Badge
A live badge classifies the solution and adds a strength description, from strongly acidic through neutral to strongly basic.
12 Common Presets
One-click pH values for everyday solutions: battery acid, lemon juice, vinegar, coffee, milk, pure water, blood, sea water, baking soda, ammonia, and bleach.
Strong Acid & Base pH
Calculate pH for fully dissociating species such as HCl, HNO₃, H₂SO₄, NaOH, KOH, and Ba(OH)₂, with the correct n-factor for multi-protic ones.
Weak Acid & Base pH
Solve the equilibrium with the full quadratic formula — no simplifying approximations — for accurate weak-acid and weak-base results.
Built-in Ka / Kb Values
Pick from common substances (acetic acid, formic acid, ammonia, and more) to auto-fill Ka or Kb, or enter your own custom constant.
Step-by-Step Solutions
Every Solution pH result includes a detailed breakdown of the equilibrium expression, substitution, quadratic setup, and final pH.
Scientific Notation Input
Type very small concentrations and constants as 1.8e-5 or 1.8×10^-5 — the calculator parses them automatically.
Runs Entirely Offline
All conversions and solution math happen locally in your browser, with no data sent anywhere.
Frequently Asked Questions
How do you calculate pH from concentration?
For a strong acid that fully dissociates, [H⁺] equals the molar concentration (times the n-factor for multi-protic acids), and pH = -log[H⁺]. In Solution pH mode, choose Strong Acid, enter the concentration, and the calculator applies this directly. For a weak acid you also need its Ka, since only part of it dissociates.
How do I find pH from Ka or pKa?
Select Weak Acid in Solution pH mode, pick a substance to auto-fill its Ka (or enter a custom value), and add the concentration. The calculator solves Ka = x² / (C − x) with the full quadratic formula to find [H⁺], then computes pH = -log[H⁺]. If you have pKa instead, convert it with Ka = 10-pKa before entering.
What is the difference between pH and pOH?
pH measures the hydrogen ion concentration [H⁺], while pOH measures the hydroxide ion concentration [OH⁻]. They are linked by pH + pOH = 14 at 25°C, so a low pH means high acidity and a low pOH means high basicity. Enter either one in Quick Convert and the other is filled in for you.
How is the pH of a strong acid different from a weak acid?
Strong acids like HCl and HNO₃ dissociate completely, so [H⁺] follows directly from the concentration. Weak acids like acetic acid only partially dissociate, reaching an equilibrium described by Ka. That is why this calculator solves a quadratic equation for weak species rather than reading [H⁺] straight off the concentration.
What are Ka and Kb values?
Ka, the acid dissociation constant, measures how much a weak acid dissociates in water — a larger Ka means a stronger weak acid. Kb is the equivalent for weak bases. These values are substance-specific and temperature-dependent; the built-in values in this calculator are for 25°C.
Why does the pH scale run from 0 to 14?
The scale comes from the auto-ionization of water: at 25°C, [H⁺] × [OH⁻] = 10-14 (the water constant Kw). Since pH = -log[H⁺] and [H⁺] ranges from about 1 M (pH 0) to 10-14 M (pH 14) in aqueous solutions, the practical range is 0–14. Very concentrated solutions can fall below 0 or above 14.
How accurate are the calculations?
Results are shown to four decimal places using standard logarithmic and quadratic formulas. Weak acid and base calculations solve the full quadratic with no simplifying approximation, so they stay accurate even for dilute solutions or species with relatively large Ka values.
Is my data private?
Yes. Every calculation runs entirely in your browser, and nothing you enter is sent to any server.
No comments yet. Be the first to comment!