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Henderson-Hasselbalch Calculator — Buffer pH from pKa

Buffer pH = pKa + log([A⁻]/[HA]) — forward and reverse, acetate/phosphate/Tris/bicarbonate presets — browser-only

  • Runs locally
  • Category Calculator
  • Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.
Common buffer pairs

Units only need to match — the ratio is what counts.

Buffer pH
4.76
When [A⁻] = [HA] the log term is 0, so pH equals pKa — the centre of the buffer range, where capacity is greatest.

What this tool does

Free Henderson-Hasselbalch calculator for buffer chemistry. The equation pH = pKa + log([A⁻]/[HA]) ties the pH of a buffer to the pKa of the weak acid and the ratio of conjugate base to acid. Enter pKa, the conjugate base concentration [A⁻] and the weak acid concentration [HA] to read the buffer pH, or switch to reverse mode and give a target pH plus pKa to get the base/acid ratio you need to mix. Only the ratio enters the log, so any consistent units work: mol/L, millimoles, even masses when the molar mass cancels. Preset pairs seed the pKa for acetate (4.76), phosphate (7.21), Tris (8.06) and bicarbonate (6.1). The tool spells out the rule every student needs: when [A⁻] = [HA] the log term is zero and pH equals pKa, the centre of the buffer range where capacity is greatest. One-click copy and a shareable URL that reopens your exact buffer. 100% client-side, no upload, no account.

Tool details

Input
Numbers
The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output
Live result + Copy
The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy
Browser-side processing
The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share
Shareable URL state
Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget
Initial JS <= 9 KB
No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit
Calculator · Student
Category and role tags drive related tools, internal links, and quick fit checks.

How to use

  1. 1. Input

    Paste or drop your content into the tool panel.

  2. 2. Process

    Click the button. All processing is local in your browser.

  3. 3. Copy / Download

    Copy the result or download to disk in one click.

How Henderson-Hasselbalch Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

  • Getting a realistic range before a purchase, plan, workout, or schedule decision.
  • Comparing scenarios by changing one input at a time.
  • Turning rough assumptions into a number you can discuss.

Calculation checks

  • Double-check units, dates, rates, and rounding assumptions.
  • Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
  • Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

  1. 1 Dilution Calculator Solve C1V1 = C2V2 and ratio dilutions (1:10) — stock + water amounts in mL / L / fl oz / gal — browser-only Open
  2. 2 pH Calculator pH, pOH, [H+] and [OH-] from any one value, with an acid/base verdict and a 0-14 colour scale, all in your browser Open
  3. 3 Molar Mass Calculator Type any chemical formula — get molar mass, a per-element mass-percent table, and mass↔mole conversion. IUPAC weights, browser-only. Open

Real-world use cases

  • Mix a buffer to a target pH in the lab

    You need an acetate buffer at pH 5.0 for an enzyme assay. Switch to reverse mode, type pH 5.0 and pKa 4.76, and read the base/acid ratio of about 1.74:1. Scale that against your total buffer concentration to get the moles of sodium acetate and acetic acid to weigh, then check your work by flipping to forward mode and confirming the pH lands back on 5.0 before you touch the pH meter.

  • Check homework on weak acid buffers

    A problem set gives pKa 7.21, 0.2 M phosphate dibasic and 0.1 M monobasic and asks for the pH. Enter the three numbers and the tool returns 7.51, with the reminder that a 2:1 base:acid ratio sits half a log unit above the pKa. Seeing the equation written out next to the answer is faster than re-deriving which way the log goes every time.

  • Teach the pH = pKa idea with live numbers

    Demonstrating buffer capacity to a class, set base and acid equal and show the pH snapping to the pKa, then nudge the ratio and watch pH drift. Share the URL so every student opens the same buffer on their own laptop and can change one number at a time to feel how the log term responds. No install, works on a phone in the back row.

  • Pick the right buffer for a pH target

    You want to hold a reaction near pH 8. Tap the Tris preset (pKa 8.06) and confirm a near 1:1 ratio lands you right there, then compare against phosphate (7.21) to see it would need an awkward base-heavy ratio and weaker buffering. The presets make it a two-tap comparison instead of three log calculations on scratch paper.

Common pitfalls

  • Swapping [A⁻] and [HA] in the ratio. The conjugate base goes on top and the weak acid on the bottom; reversing them flips the sign of the log term, so a buffer you meant to be above the pKa comes out below it. Acetate base over acetic acid, not the other way around.

  • Forgetting the equation only sets pH, not capacity. A 0.001 M buffer and a 0.5 M buffer at the same ratio read the same pH here, but the dilute one is overwhelmed by a tiny addition of acid. Set the ratio for pH, then choose the absolute concentration for the capacity you need.

  • Using a pKa far from the target pH. Outside roughly pKa ± 1 the ratio gets extreme (more than 10:1) and the buffer barely resists change. If the tool tells you to mix 50:1 base to acid, that is a sign you picked the wrong buffer pair, not that the numbers are wrong.

Privacy

Every step — the Henderson-Hasselbalch formula, the log, the reverse ratio — is plain JavaScript that runs in your browser tab. No pKa, concentration or pH you enter ever leaves the page, and nothing is logged. The one caveat: the shareable URL encodes your inputs in the query string, so a share link pasted into chat records those numbers in the recipient server's access log. For unpublished research values, use the copy button and paste the text rather than sharing the URL.

FAQ

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Made by Toolora · 100% client-side · Updated 2026-05-30