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What is pH Calculator?

A pH Calculator computes ph from the inputs you provide. It applies the standard formula to the values you enter and returns the result instantly, without sending any data to a server. Free pH Calculator. The tool runs entirely in.

pH Calculator

pH = -log[H+]. 7 neutral, <7 acidic, >7 basic. Each unit = 10×.

Inputs

M [H+]

pH

-

Breakdown

[H+]
-
[OH-]
-
pOH
-
Category
-

About

pH measures hydrogen ion activity. pH = -log10[H+]. Pure water: 7 (neutral). Vinegar: 2.5. Lemon: 2. Stomach acid: 1.5. Blood: 7.4. Soap: 9-10. Bleach: 13. pH + pOH = 14 in dilute aqueous solutions.

Formula

pH = -log[H+]; [H+] = 10^(-pH); pOH = 14 - pH

Frequently asked questions

How accurate is the pH Calculator?

It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.

Is the pH Calculator free to use?

Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.

Are my inputs saved anywhere?

No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.

Can I use the pH Calculator on my phone?

Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.

Does the pH Calculator work offline?

Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.

How do I report a bug or suggest improvement to the pH Calculator?

Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.

Can I share results from the pH Calculator?

Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.

Why are the results different from another ph tool?

Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.

Is the pH Calculator accurate?

The pH Calculator applies the standard formula for ph. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.

Is the pH Calculator free?

Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.

Are my inputs saved?

No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.

How to use the pH Calculator

The pH Calculator is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:

  • Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
  • Speed: results update as you type. No network round trip.
  • Offline use: once the page is cached, it works without internet.
  • No signup: no account, no email, no rate limits.

Step by step

  1. Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
  2. Read the result as it updates. The number reflects the formula commonly accepted in pH-related calculations.
  3. Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
  4. Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.

When you would use this

  • Quick estimates: when you need a number now and don't want to open a spreadsheet.
  • Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
  • Comparison: running the same calculation with different inputs to compare options side by side.
  • Learning: building intuition for how the underlying math behaves.
  • Documentation: capturing a snapshot of inputs and outputs at a point in time.

The formula explained

This calculator uses the following formula:

pH = -log[H+]; [H+] = 10^(-pH); pOH = 14 - pH

The reason this formula works is rooted in the underlying physics, finance, or biology of the problem. Behind every calculator is a published, peer-reviewed equation or a widely accepted convention. We do not invent formulas; we apply standard ones from textbooks, government tables, professional bodies, and academic literature.

If you are curious about the math, the simplest way to verify is to plug in two known numbers and compare against a known result. The calculator should match published examples to within rounding precision.

How the pH scale works

pH = -log10[H+]. Because the scale is logarithmic, pH 4 is ten times more acidic than pH 5. Soren Sorensen introduced the notation at the Carlsberg Laboratory in 1909. At 25 C, pH + pOH = 14, and pure water sits at pH 7.00.

pH    = -log10[H+]      [H+] = 10^(-pH)
pOH   = 14 - pH         Kw   = [H+] x [OH-] = 1.0 x 10^-14
Worked example: 5 percent vinegar has [H+] near 1.7 x 10^-3 mol/L, giving pH 2.77. A tenfold dilution lifts it to pH 3.77.

Reference pH of common substances

SubstanceTypical pHCategory
Stomach acid1.5 to 2.0Strong acid
Lemon juice2.0 to 2.6Strong acid
Vinegar2.4 to 3.4Weak acid
Black coffee4.5 to 5.0Weak acid
Pure water (25 C)7.0Neutral
Human blood7.35 to 7.45Weak base
Seawater7.5 to 8.4Weak base
Household ammonia11.0 to 11.5Strong base
Bleach12.5 to 13.0Strong base

Pitfalls

  • Ignoring temperature. Kw rises with heat; a reading at 40 C from a meter calibrated at 25 C reads about 0.1 unit low.
  • Stale buffer. Open buffer bottles absorb carbon dioxide and drift acidic within weeks. Recalibrate monthly.
  • Treating pH as linear. Plan dilutions on the log scale: each unit is a tenfold change in [H+].
  • Measuring pure water with a standard electrode. Too few ions, conductivity too low, readings drift. Add salt or use a low-ionic-strength probe.

Related calculators

FAQ

Why is pure water not always pH 7?

Contact with air absorbs carbon dioxide and forms carbonic acid, drifting pH toward 5.6. Kw is also temperature dependent, so hot water shifts neutral pH downward by 0.5 to 1.0 unit even though it is not truly acidic.

What is the link between pH and pKa?

Henderson-Hasselbalch: pH = pKa + log10([A-]/[HA]). When pH equals pKa, a weak acid is half dissociated. Buffers work best within one unit of pKa, which is why phosphate (pKa 7.21) dominates biological work.

Can pH go below 0 or above 14?

Yes in concentrated solutions. 12 molar HCl has pH near minus 1.1, saturated sodium hydroxide reaches pH 15. The 0 to 14 range is a dilute-aqueous convention, not a physical limit.

How do I adjust pool or aquarium pH safely?

Move no faster than 0.2 unit per day for fish tanks and 0.5 for pools. Use muriatic acid or carbon dioxide to lower, sodium carbonate to raise. Dose, wait 4 to 6 hours, retest, then dose again.

Sources: IUPAC Recommendations on the Measurement of pH (2002); Harris, Quantitative Chemical Analysis (2020); US EPA Method 9040C. Last updated 2026-05-28.