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Henderson-Hasselbalch calculator

Work with the Henderson-Hasselbalch equation pH = pKa + log₁₀([A⁻]/[HA]) for buffer solutions. Find the pH of a buffer, the base-to-acid ratio needed to hit a target pH, or the pKa from a measured pH — the everyday maths of preparing biological and chemical buffers.

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The Henderson-Hasselbalch calculator turns Find, pKa of the weak acid, Conjugate base [A⁻], Weak acid [HA], Target pH (ratio mode), Measured pH (pKa mode) into Result, Base : acid ratio, instantly and for free. For instance, with Find = pH of the buffer, pKa of the weak acid = 4.76, Conjugate base [A⁻] = 0.1, Weak acid [HA] = 0.1, Target pH (ratio mode) = 5 and Measured pH (pKa mode) = 7.51 it returns Result = 4.76 and Base : acid ratio = 1.000 : 1.

How to use it

  1. Enter your values: Find, pKa of the weak acid, Conjugate base [A⁻], Weak acid [HA], Target pH (ratio mode), Measured pH (pKa mode).
  2. Read the result instantly: Result, Base : acid ratio.

Frequently asked questions

How does the Henderson-Hasselbalch calculator work?

It takes Find, pKa of the weak acid, Conjugate base [A⁻], Weak acid [HA], Target pH (ratio mode) and Measured pH (pKa mode) and derives Result and Base : acid ratio from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

6 values: Find, pKa of the weak acid, Conjugate base [A⁻], Weak acid [HA], Target pH (ratio mode) and Measured pH (pKa mode). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Find = pH of the buffer, pKa of the weak acid = 4.76, Conjugate base [A⁻] = 0.1, Weak acid [HA] = 0.1, Target pH (ratio mode) = 5 and Measured pH (pKa mode) = 7.51, the calculator returns Result = 4.76 and Base : acid ratio = 1.000 : 1. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Find = Ratio for a target pH, pKa of the weak acid = 9.52, Conjugate base [A⁻] = 0.2, Weak acid [HA] = 0.2, Target pH (ratio mode) = 10 and Measured pH (pKa mode) = 15.02 instead, Result goes from 4.76 to 3.02 — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which “Find” option should I choose?

You can pick between « pH of the buffer », « Ratio for a target pH » and « pKa from measured pH ». Each one changes what the calculator works out, so switch and compare — the default is « pH of the buffer ».

What does it give for smaller values?

Scaled down to Find = pH of the buffer, pKa of the weak acid = 2.38, Conjugate base [A⁻] = 0.05, Weak acid [HA] = 0.05, Target pH (ratio mode) = 2.5 and Measured pH (pKa mode) = 3.76, Result comes out at 2.38. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Preparing a solution at a stated concentration, working out how much of a reagent a reaction needs, and converting between mass, moles and volume.

What is the most common mistake?

Confusing molarity with molality. One is per litre of solution and the other per kilogram of solvent; they diverge as concentration rises, and only one of them is temperature-independent.

What is the difference between the Henderson-Hasselbalch calculator and the Titration calculator?

This one returns Base : acid ratio; the Titration calculator returns Unit and Moles of titrant equivalents. That is the whole difference — open the one whose figure you need.

Where do the figures come from, and how current are they?

Atomic masses are the IUPAC standard values. Results assume ideal behaviour and standard conditions unless the tool says otherwise — real solutions deviate, and lab work needs lab measurement.

Further reading

All guides →
How-toHow to Calculate pH — And When the Weak-Acid Shortcut Stops WorkingFour routes for four kinds of solution, each worked with real numbers. Including the part most pages leave out: the square-root formula for a weak acid is an approximation with a validity limit, and it fails quietly.How-toHow to Calculate a Dilution with C1V1 = C2V2Solve for the missing term, then convert the answer into a bench instruction. The step almost everyone skips is that the solvent you add is V2 minus V1, not V2.ExplainerThe Ideal Gas Law Explained: PV = nRT, R in Every Unit, and Where It BreaksPV = nRT holds when the gas is dilute and far from condensing. The value of R depends entirely on the units you feed it, and the temperature is never in degrees Celsius.ExplainerHow Half-Life Works: What Is Left After 1, 3 and 10 Half-LivesOne half-life leaves 50%, three leave 12.5%, ten leave less than a tenth of a percent. The formula is a single line — the part worth understanding is why the answer never reaches zero.How-toHow to Solve Stoichiometry Problems: Grams to Moles to Ratio to GramsEvery problem in the chapter is the same four moves. The mole ratio is the hinge, and it is the step students lose — worked here end to end, limiting reactant and percent yield included.How-toHow to Calculate Molar Mass, Including Parentheses and HydratesMultiply each atomic weight by its subscript and add. The only three places the arithmetic goes wrong are a subscript after a closing bracket, the hydrate dot, and a capital letter typed as a lowercase one.