pH & Dilution Calculator
Convert between pH, pOH, [H+] and [OH-] and solve C1V1 = C2V2 dilutions with any unit.
pH converter
Strong acid or base at 25 °C — the other three values update as you type.
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- pH
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- pOH
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- [H+] mol/L
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- [OH-] mol/L
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Dilution calculator (C1V1 = C2V2)
Leave exactly one box empty and it is solved for you. C1/V1 are the stock, C2/V2 the final diluted solution.
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- Dilution factor
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- Solvent to add
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- Equation
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How it works
The pH converter uses the definitions pH = −log₁₀[H⁺] and [H⁺] = 10−pH, plus the water constant pH + pOH = 14 at 25 °C (Kw = 1.0 × 10⁻¹⁴ mol²/L²). Type any one of the four values — pH, pOH, [H⁺] or [OH⁻] — and the other three are recalculated instantly, together with a verdict on the acid/base scale. These relations describe strong acids and bases that dissociate completely; for a weak acid you need its Ka as well.
The dilution calculator solves the classic C1V1 = C2V2 relationship: the moles of solute you take out of the stock bottle equal the moles in the final diluted solution, so concentration times volume is conserved. Leave one of the four boxes empty and it is solved for you, in the unit you picked; the tool also reports the dilution factor and how much solvent to add (V2 − V1). Everything runs in plain JavaScript in your browser — nothing you type is uploaded, stored or shared.
Frequently asked questions
How do you calculate pH from concentration?
pH is the negative base-10 logarithm of the hydrogen ion concentration: pH = -log₁₀[H⁺], and the reverse is [H⁺] = 10^-pH. Pick "[H+]" in the converter and type a molarity — 0.001 mol/L gives pH 3.00 — or pick "pH" and the tool works backwards to the ion concentrations. At 25 °C the water constant Kw = 1.0 × 10⁻¹⁴ mol²/L² ties the pair together, so pH + pOH = 14 and [H⁺] × [OH⁻] = 10⁻¹⁴. These formulas assume a strong acid or base that dissociates completely; a weak acid such as acetic acid also needs its Ka, because only a small fraction of the molecules release their proton.
How do I use the C1V1 = C2V2 dilution formula?
C1V1 = C2V2 says the amount of solute you pipette out of the stock bottle is the same amount that ends up in the diluted solution, so concentration times volume stays constant. C1 and V1 are the concentration and volume of the stock, C2 and V2 the final concentration and volume. Enter any three of the four values, leave the fourth box empty, and the calculator rearranges the equation for you — for example 1 M stock diluted to 0.1 M in a final 100 mL needs V1 = (0.1 × 100) / 1 = 10 mL of stock. Each box has its own unit selector (M, mM, µM, nM and L, mL, µL) so you can mix a millimolar stock with a microlitre volume without converting anything by hand.
What does a 1:10 dilution mean and how much solvent do I add?
A 1:10 dilution means the final solution is ten times weaker than the stock: one part stock plus nine parts solvent, giving a dilution factor of 10 (C1 ÷ C2, which is also V2 ÷ V1). The volume of solvent you actually add is V2 − V1, not V2, because the stock already contributes volume — for 10 mL of stock brought to 100 mL you add 90 mL of water or buffer. The calculator shows the dilution factor and that solvent volume for every result, and it flags the case where the final volume is smaller than the starting volume, which means you are concentrating rather than diluting.