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pH Calculator

Science & Engineering

pH, pOH, H+ concentration and acid dilution

Quick Answer

pH Calculator: pH, pOH, H+ concentration and acid dilution. pH = −log₁₀[H⁺]; [H⁺] = 10^(−pH) mol/L.

mol/L
pH
3.00
Acidic

Calculation steps

  1. 1pH = −log₁₀[H⁺] (base-10 logarithm)
  2. 2pH = −log₁₀(0.001) = 3.00
  3. 3pOH = 14 − pH = 11.00 (at 25°C)

Position on pH scale

Acidic
Neutral
Alkaline

pH 3.00

pOH11.00
[OH⁻]1.00e-11 mol/L

Common substances pH

SubstancepHClass
Stomach acid1.5Acidic
Lemon juice2.4Acidic
Vinegar2.9Acidic
Cola2.5Acidic
Coffee5.0Acidic
Pure water7.0Neutral
Blood7.4Neutral
Seawater8.1Alkaline
Soapy water10.0Alkaline
Ammonia11.5Alkaline
Bleach12.5Alkaline
Drain cleaner13.5Alkaline
pH is logarithmic: each step is a 10× change in [H⁺]. Lemon juice (pH 2.4) has about 100,000× more hydrogen ions than blood (pH 7.4). Blood pH is tightly buffered at 7.35–7.45; below 7.35 is acidosis, a medical emergency. The formula assumes 25°C — at 100°C neutral water is pH 6.14.

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How to Use

  1. Enter known quantities: fill values and confirm units in the pH Calculator.
  2. Instant solution: unknowns solve live with the formula shown transparently.
  3. Use constant/material tables: standard physical constants and material data are listed on this page.
  4. Compare conditions: change inputs to compare scenarios.

Key Points

  • pH Calculator is a free online science & engineering tool — open and use, no sign-up.
  • All calculations run locally in your browser; your data never leaves the device.
  • Key capability: pH, pOH, H+ concentration and acid dilution.
  • Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

pH and hydrogen-ion concentration

pH = −log₁₀[H⁺]; [H⁺] = 10^(−pH) mol/L
At 25°C: pH + pOH = 14
pH<7 acidic, =7 neutral, >7 alkaline; each unit is a 10× change
Strong-acid dilution: C₁V₁ = C₂V₂
Weak acids/bases need Ka — this formula does not apply

Example: [H⁺] = 0.001 mol/L → pH 3; dilute 10× → pH 4; pH 9 → pOH 5, [OH⁻] = 10⁻⁵.

FAQ

How do I use the pH Calculator?
Open the page and fill in the input fields — results update automatically. pH, pOH, H+ concentration and acid dilution.
Are the results accurate?
Yes. Standard formulas and conversion factors are used and verified.
Is it free? Do I need to sign up?
Completely free. No registration, login or download required.
Does it work on mobile?
Yes. The responsive design works on phones, tablets and desktops.
Is my data saved?
No. Everything runs locally in your browser.

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Source & Updates

Based on CODATA recommended constants and standard physics formulas. Last updated: 2025-07

Last updated:

Formulas and content on this page are reviewed by the YiJianSuan team. For reference only — official sources prevail.

Maintained and periodically reviewed by the YiJianSuan editorial team — review process in ourEditorial Policy.

Cite this page: YiJianSuan. pH Calculator[EB/OL]. https://www.yijiansuan.com/en/c/science/ph

Results provided by this tool are for reference only and do not constitute professional advice.