# pH Calculator

Convert between pH, [H+], pOH and [OH-], or compute pH from a strong acid/base concentration, including dilution.

> Canonical page: https://elysiatools.com/en/tools/ph-calculator

- **Category:** Math & Numbers

- **Keywords:** ph, h+, oh-, poh, acidity, strong acid, strong base, dilution, chemistry

## Overview

The pH Calculator is a chemistry utility designed to convert between pH, hydrogen ion concentration [H+], pOH, and hydroxide ion concentration [OH-]. It also computes the pH of strong acids and bases based on their molar concentration and proton/hydroxide count, and calculates the resulting pH after dilution with water.

## Inputs

- **Calculation Mode** (select)
- **Input Quantity** (select): Which of the four quantities you are entering.
- **Input Value** (number): Numeric value of the selected input quantity.
- **Acid/Base** (select)
- **Proton/Hydroxide Count (n)** (number): Number of H+ per acid molecule (HCl=1, H2SO4=2) or OH- per base unit (NaOH=1, Ba(OH)2=2).
- **Concentration C (mol/L)** (number): Molar concentration of the acid or base (mol/L).
- **Initial Volume V1 (mL)** (number): Initial volume of the acid/base solution before dilution.
- **Added Water V2 (mL)** (number): Volume of pure water added to dilute the solution.
- **Decimal Places** (number)

## When to use

- When you need to quickly convert between pH, pOH, \[H+\], and \[OH-\] concentrations without manual logarithmic calculations.
- When determining the pH of a strong acid or strong base solution of a known molar concentration and chemical formula.
- When calculating the final pH of an acidic or basic solution after adding a specific volume of pure water.

## How it works

- Select the calculation mode: conversion, strong acid/base pH calculation, or dilution.
- Enter the input values, such as the initial concentration, proton/hydroxide count, or starting pH.
- Specify dilution volumes (initial volume and added water) if calculating a diluted solution.
- Click calculate to instantly view the resulting pH, pOH, \[H+\], \[OH-\], and solution nature (acidic, basic, or neutral).

## Use cases

- Preparing laboratory reagents by calculating the exact pH of a strong acid or base solution before an experiment.
- Verifying homework or exam answers in chemistry courses involving pH, pOH, and ion concentration conversions.
- Determining the pH change in industrial chemical mixtures when diluting stock solutions with water.

## Frequently asked questions

### What temperature is assumed for the calculations?

The calculator assumes a standard temperature of 25 °C, where the water autoionization constant (Kw) is 1.0 x 10^-14.

### How does the proton/hydroxide count affect the pH calculation?

It accounts for polyprotic strong acids (like H2SO4, n=2) or bases (like Ba(OH)2, n=2) that release multiple ions per molecule, multiplying the effective concentration.

### Can this calculator be used for weak acids or weak bases?

No, this calculator is designed for strong acids and bases that dissociate completely; it does not use Ka or Kb values.

### What units are used for concentration and volume?

Concentration is measured in moles per liter (mol/L or M), and volumes for dilution are measured in milliliters (mL).

### How does dilution affect the pH of a strong acid?

Adding water decreases the concentration of H+ ions, moving the pH closer to neutral 7.

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