Neutralization Calculator (volume or mass of base to neutralise an acid)

Understanding the neutralization calculator — concept and principle

This calculator finds how much base solution, or how much solid base, is needed to neutralise a given amount of acid, counting how many H⁺ each acid formula releases and how many each base formula accepts. It also gives the millimoles involved and the total volume at neutralisation. It is used for titration planning, lab preparation and chemistry homework.

Neutralisation is reached when moles of OH⁻ equal moles of H⁺, whatever the volumes.

How it is calculated

At equivalence: n_H × C_acid × V_acid = n_OH × C_base × V_base

V_base = n_H C_a V_a ÷ (n_OH C_b)

Solid base mass (g) = mmol of base ÷ 1,000 × molar mass

Concentrations in mol/L and volumes in mL, so mol/L × mL gives mmol.
n_H is the number of acidic hydrogens per acid formula (1 for HCl, 2 for H₂SO₄); n_OH the H⁺ accepted per base formula.

The principle

Neutralisation pairs each H⁺ from the acid with one OH⁻ (or other proton acceptor) from the base. The equivalence point is reached when the amounts are equal. Since amount = concentration × volume, equating the two sides gives the volume of base needed. For acids that release more than one proton, all acidic hydrogens are counted.

Worked example

Default inputs: 0.5 mol/L acid, 25 mL, 1 H⁺ per formula; 0.2 mol/L base, 1 OH⁻ per formula; base molar mass 40.00 g/mol (NaOH).

H⁺ to neutralise = 0.5 × 25 × 1 = 12.5 mmol.
Base needed = 12.5 ÷ 1 = 12.5 mmol.
Base volume = 12.5 ÷ 0.2 = 62.5 mL.
Or solid NaOH = 12.5 ÷ 1,000 × 40.00 = 0.5 g.
Total volume at neutralisation = 25 + 62.5 = 87.5 mL.

Each point is the calculator re-run with only “Base concentration (mol/L)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Base concentration (mol/L)	Base volume needed (mL)
0.05	250
0.1	125
0.15	83.33
0.2	62.5
0.25	50
0.3	41.67
0.4	31.25

How to read the result

This is the stoichiometric amount, not a pH. The solution is at pH 7 at equivalence only for a strong acid with a strong base; with a weak acid and strong base it ends slightly basic, and with a weak base and strong acid slightly acidic. Choose an indicator whose colour change matches the expected equivalence pH.

Common mistakes

Forgetting the second H⁺ of sulfuric acid.
Mixing mL and L.
Assuming pH 7 at equivalence for weak acids or bases.
Using a solid base that has absorbed moisture or carbon dioxide, which makes it weaker than its label.

Keep in mind: Neutralising concentrated acids and bases releases heat and can splash. Add slowly, wear eye protection and follow laboratory safety rules.

Frequently asked questions

How much NaOH neutralises 1 mol of H₂SO₄?

2 mol, because sulfuric acid releases two protons.

Is the equivalence point always at pH 7?

No, only for strong acid with strong base.

What is a millimole?

One thousandth of a mole; mol/L × mL gives mmol.

Can ammonia neutralise an acid?

Yes; each NH₃ accepts one H⁺.

Sources: OpenStax, Chemistry 2e (2019), sections 4.5 "Quantitative Chemical Analysis" and 14.7 "Acid-Base Titrations"

Checked 9 Nov 2026. Acid–base neutralisation stoichiometry (moles of H⁺ = moles of OH⁻ at the equivalence point): OpenStax, Chemistry 2e (2019), §4.5 “Quantitative Chemical Analysis” and §14.7 “Acid-Base Titrations” — standard method. Molar masses from IUPAC atomic weights.

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