Acid-Base Titration Calculator

Background.

An acid-base titration calculator converts raw burette and pipette readings — the concentration of a standardised titrant, the volume of titrant delivered to the equivalence point, and the volume of the unknown solution titrated — into the concentration of an unknown acid or base. Titration is one of the oldest and still most widely used quantitative techniques in chemistry: a solution of precisely known concentration (the titrant) is added incrementally to a measured volume of unknown solution (the analyte) until an indicator changes colour or a pH meter registers the steep inflection that marks the equivalence point, the moment at which the titrant has reacted with the analyte in exactly the stoichiometric proportions of the balanced neutralisation equation.

The defining design choice of this calculator, and the reason it exists as a dedicated tool rather than being folded into the molarity or pH calculators, is that it treats the stoichiometric ratio between titrant and analyte as an explicit input rather than assuming every titration is a simple 1:1 acid-base pair. That assumption is safe for the textbook case of a monoprotic acid like acetic acid (CH3COOH) reacting with a monoprotic base like sodium hydroxide (NaOH), where one mole of acid consumes exactly one mole of base. It silently fails for a diprotic acid like sulfuric acid (H2SO4), which requires two moles of NaOH per mole of acid at its second equivalence point, or for a diprotic base like sodium carbonate (Na2CO3), which requires two moles of HCl per mole of base. A calculator that hardcodes a 1:1 ratio will report exactly double the correct concentration for those common polyprotic systems — an error large enough to fail a quality-control specification or invalidate a student lab report, and one that is easy to miss because the arithmetic 'looks' right.

Acid-base titration is standard practice across analytical chemistry, pharmaceutical quality control, food and beverage testing (measuring the acidity of wine, vinegar, or citrus juice), environmental water testing (alkalinity and acidity determinations), and introductory chemistry education. Before a titrant can be trusted to determine an unknown, it must itself be standardised — its exact concentration determined by titrating it against a primary standard, a solid reagent pure and stable enough that its mass alone determines the moles present. The U.S. National Institute of Standards and Technology (NIST) certifies primary acidimetric standards including potassium hydrogen phthalate (KHP), benzoic acid, and boric acid for standardising bases, and sodium carbonate for standardising acids, each assayed to better than 0.01 percent uncertainty precisely so that every titration performed with a solution standardised against them inherits that traceability back to a national metrology laboratory.

This calculator assumes the titration has already been performed correctly — a suitable indicator or pH-meter endpoint chosen to coincide closely with the true equivalence point, the burette read to its full precision, and the titrant itself standardised against a primary standard — and focuses purely on the arithmetic conversion from burette reading to concentration. Below the calculator you will find the full derivation of the working equation from the definitions of molarity and reaction stoichiometry, a worked example determining the concentration of acetic acid in a diluted vinegar sample, a second worked example demonstrating exactly how much a wrongly assumed 1:1 ratio distorts the answer for a diprotic acid, and guidance on reading the correct stoichiometric ratio off any balanced neutralisation equation.

What is acid-base titration calculator?

A titration is the process of determining the quantity of a substance in solution (the analyte, or 'titrand') by adding a reagent of precisely known concentration (the titrant) in small, measured increments until the reaction between them is judged to be stoichiometrically complete — the equivalence point. In acid-base titration specifically, the titrant is a strong acid or strong base of standardised concentration, and the analyte is the acid or base whose concentration is unknown. The equivalence point is where the moles of titrant delivered exactly match the moles required by the balanced neutralisation equation; the endpoint is the experimentally observed signal (an indicator colour change, or a sharp jump in a pH-vs-volume curve) that the analyst uses to approximate the equivalence point, and the small difference between the two is called titration error. At the equivalence point, the amount of titrant delivered, n_titrant = C_titrant × V_titrant, relates to the amount of analyte originally present, n_analyte, through the stoichiometric coefficients of the balanced reaction: n_analyte = n_titrant × (coefficient of analyte / coefficient of titrant), a ratio this calculator calls simply 'ratio'. Dividing n_analyte by the volume of the analyte aliquot recovers its concentration.

How to use this calculator.

1. 01Determine your titration's balanced neutralisation equation and read off the stoichiometric ratio: moles of analyte produced per mole of titrant consumed. For monoprotic acid + monoprotic base, the ratio is 1. For a diprotic acid titrated to its second equivalence point with a monoprotic base (or a diprotic base titrated with a monoprotic acid), the ratio is 0.5.
2. 02Enter the titrant's standardised concentration in mol/L.
3. 03Enter the volume of titrant delivered to the equivalence point, read from the burette, in mL.
4. 04Enter the volume of the unknown/analyte aliquot that was pipetted into the flask before titrating, in mL.
5. 05Enter the stoichiometric ratio determined in step 1.
6. 06Read the primary result, the unknown analyte concentration in mol/L, plus the intermediate moles of titrant and moles of analyte for your lab notebook.
7. 07If your titration has multiple equivalence points (a polyprotic acid or base), run the calculator once per equivalence point you use, with the titrant volume measured to that specific equivalence point and the matching stoichiometric ratio.

The formula.

At the equivalence point of a titration, the moles of titrant delivered are n_titrant = C_titrant × V_titrant, using the titrant's standardised concentration and the burette reading (converted to litres). The balanced neutralisation equation between the titrant and the analyte fixes a stoichiometric relationship between how many moles of each react: if the equation is written a·Analyte + b·Titrant → products, then every b moles of titrant consumed corresponds to exactly a moles of analyte, so n_analyte = n_titrant × (a/b). This calculator calls the ratio (a/b) simply 'ratio' — moles of analyte per mole of titrant. For the common monoprotic-acid-vs-monoprotic-base case (a = b = 1), ratio = 1 and n_analyte = n_titrant exactly. For sulfuric acid titrated with sodium hydroxide to its second equivalence point (H2SO4 + 2 NaOH → Na2SO4 + 2 H2O, so a = 1, b = 2), ratio = 1/2 = 0.5, meaning only half as many moles of analyte are present as moles of titrant delivered.

Once n_analyte is known, the analyte's original concentration follows from the same C = n/V relationship used to standardise the titrant in the first place: C_unknown = n_analyte / V_unknown, where V_unknown is the volume of the analyte aliquot (converted to litres). Substituting the full chain gives the single working equation this calculator implements: C_unknown = (C_titrant × V_titrant × ratio) / V_unknown, where V_titrant and V_unknown may both be entered in millilitres because the unit conversion (dividing each by 1000) cancels identically in the numerator and denominator.

The practical consequence of skipping the ratio term, or hardcoding it to 1, is a systematic error proportional to how far the true stoichiometry departs from 1:1. For the H2SO4/NaOH example above, hardcoding ratio = 1 instead of the correct 0.5 doubles the reported concentration — not a rounding error, but a factor-of-two mistake that a plausible-looking number on a screen will not warn you about. Reading the correct ratio off the balanced equation before entering data is therefore the single most important step in using this calculator correctly.

A worked example.

Frequently asked questions.

References& sources.

1. [1]NIST — 'Evaluation of Independent High-Precision Assay Procedures for a High-Purity Primary Standard Reagent.' Describes NIST's certified acidimetric and alkalimetric primary-standard SRMs (potassium hydrogen phthalate, benzoic acid, boric acid, sodium carbonate) used to standardise titrants before use. National Institute of Standards and Technology.
2. [2]Harvey, D.T. Analytical Chemistry 2.1, §9.2 'Acid-Base Titrations' — derives the stoichiometric relationship between moles of titrant and moles of analyte, including polyprotic acid/base cases with equivalence-point ratios other than 1:1. LibreTexts / DePauw University.
3. [3]IUPAC Gold Book, 'titration' (T06387) — formal IUPAC definition of titration as the process of determining a substance's quantity by measured addition of a reacting titrant. International Union of Pure and Applied Chemistry.
4. [4]IUPAC Gold Book, 'equivalence point' (E02188) — formal definition of the equivalence point as the stage of titration at which titrant has completely reacted with titrand according to reaction stoichiometry, distinguished from the observed endpoint. International Union of Pure and Applied Chemistry.
5. [5]Skoog, D.A., West, D.M., Holler, F.J. & Crouch, S.R. (2013). Fundamentals of Analytical Chemistry, 9th ed. Cengage. Chapters on titrimetric methods, primary standards, and polyprotic acid-base equilibria. ISBN 978-0495558286.