pH Calculator
Start from pH, pOH, [H⁺] or [OH⁻] — get the full panel with log steps, a Kw check & an interactive scale of 14 household substances.
Scientific notation works: 1e-3 = 0.001.
💡 The four quantities lock together at 25 °C: pH + pOH = 14 and [H⁺] × [OH⁻] = 10⁻¹⁴. Know any one and the other three follow — that's the whole game.
🍋 Acidic · like 🫙 vinegar
pH 3
pOH
11
[H⁺]
1.00e-3
[OH⁻]
1.00e-11
Step-by-step working
1. pH = −log₁₀[H⁺] = −log₁₀(1.00e-3) = 3
2. [OH⁻] = 10^(−pOH) = 1.000e-11 mol/L
3. Check: [H⁺] × [OH⁻] = 1.00e-14 ≈ 10⁻¹⁴ = Kw ✓
🌈 The pH scale
Each step is 10× — pH 2 is ten times more acidic than pH 3. The marker shows your value.
⚠️ pH + pOH = 14 holds at 25 °C — Kw grows with temperature, so hot solutions shift the neutral point below 7. Strong-acid assumptions also break down below ~10⁻⁶ mol/L where water's own ions matter.
🧪One value in, the whole acid-base picture out
pH, pOH, [H⁺], and [OH⁻] are four faces of the same fact — at 25 °C they lock together through pH + pOH = 14 and Kw = 10⁻¹⁴. Tell this calculator whichever one you know and it returns the other three with the logarithm steps written out and a Kw self-check. Your value lands on a full-colour 0–14 scale alongside fourteen everyday substances — from battery acid to drain cleaner — each clickable to explore.
📊Everything you'd want to know
- Four starting points: pH, pOH, [H⁺], or [OH⁻] — scientific notation accepted (1e-3).
- The full panel every time, with acidic/neutral/basic verdict and a 'like lemon juice' comparison.
- Logarithm working shown step by step, ending with the [H⁺]×[OH⁻] = Kw verification.
- An interactive pH scale with 14 household reference points.
- The 10×-per-step insight: pH 2 isn't 'a bit' more acidic than pH 4 — it's 100 times.
🧮The maths
The logarithm compresses an enormous range — concentrations from 1 to 10⁻¹⁴ mol/L — into a friendly 0–14 number. The price of that compression: every single pH step hides a factor of ten in actual acidity.
💡pH intuition worth keeping
- Neutral is 7 only at 25 °C — Kw rises with temperature, so hot pure water sits slightly below 7 yet is still neutral.
- For strong acids, [H⁺] ≈ the acid concentration; weak acids ionise partially and need Ka.
- Below about 10⁻⁶ mol/L, water's own autoionisation contributes — naive −log gives silly answers for 10⁻⁸ M acid.
- pH can go below 0 and above 14 in concentrated solutions — the 0–14 scale is a convention, not a law.
💡 Frequently Asked Questions
How do I calculate pH from concentration?+
pH = −log₁₀[H⁺]. For [H⁺] = 0.001 mol/L, pH = −log(10⁻³) = 3. Enter the concentration (plain or scientific notation) and this calculator shows the log step plus pOH and [OH⁻].
What is the relationship between pH and pOH?+
They always sum to 14 at 25 °C, because [H⁺] × [OH⁻] = Kw = 10⁻¹⁴. Know either one and the other is a subtraction — the calculator uses exactly this to fill in the full panel.
Is pH 6 slightly acidic or very acidic?+
Only slightly — but remember each step is 10×: pH 6 has ten times the H⁺ of neutral water, pH 3 has ten thousand times. The scale visual places your value among everyday substances for intuition.
What is the pH of common substances?+
Lemon juice ≈ 2.4, vinegar ≈ 3, black coffee ≈ 5.5, pure water 7, sea water ≈ 8.1, baking soda ≈ 9, ammonia ≈ 11.5, bleach ≈ 13. All fourteen references on the scale are clickable to load instantly.
Can pH be negative or above 14?+
Yes — 10 M HCl has pH ≈ −1, and concentrated NaOH exceeds 14. The 0–14 range covers ordinary dilute solutions, which is why it's taught as 'the scale', but the formula itself has no limits.