Reference Electrode Potential Converter
Convert a measured potential to RHE, SHE or another reference electrode, and back.
Your potential vs RHE at pH 14
0.600 your reading+ 0.098 Hg/HgO vs SHE+ 0.829 0.0592 × pH 14
The red line is your potential. Each ruler counts it from its own zero.
- Hg/HgO, 1 M KOH: The figure most papers use. At pH 14 it puts Hg/HgO 0.927 V above RHE, in line with the 0.923 to 0.927 V labs measure. Some papers use +0.094 to +0.108 V.
This potential on every scale
- RHE at pH 14
- +1.527 V
- Standard hydrogen (SHE)
- +0.698 V
- Ag/AgCl, saturated KCl
- +0.501 V
- Ag/AgCl, 3.5 M KCl
- +0.493 V
- Ag/AgCl, 3 M KCl
- +0.488 V
- Ag/AgCl, 1 M KCl
- +0.463 V
- Saturated calomel (SCE)
- +0.457 V
- Hg/HgO, 1 M KOH (your reading)
- +0.600 V
- Hg/HgO, 1 M NaOH
- +0.590 V
- Hg/Hg₂SO₄, saturated K₂SO₄
- +0.058 V
- Hg/Hg₂SO₄, 0.5 M H₂SO₄
- +0.018 V
The formula
A potential measured against a reference electrode converts to the reversible hydrogen electrode scale at 25 °C with E(RHE) = E(measured) + E(reference vs SHE) + 0.0592 × pH. Without the pH term, the same sum gives the potential against SHE.
Reference electrode potentials at 25 °C
| Electrode | vs SHE | Use in |
|---|---|---|
| Ag/AgCl, saturated KCl | +0.197 V | Neutral and acidic solutionsPublished figures run from +0.195 to +0.199 V. |
| Ag/AgCl, 3.5 M KCl | +0.205 V | Neutral and acidic solutions |
| Ag/AgCl, 3 M KCl | +0.210 V | Neutral and acidic solutions |
| Ag/AgCl, 1 M KCl | +0.235 V | Neutral and acidic solutions |
| Saturated calomel (SCE) | +0.241 V | Aqueous solutions, corrosion workPublished figures run from +0.241 to +0.244 V. |
| Hg/HgO, 1 M KOH | +0.098 V | Alkaline solutionsThe figure most papers use. At pH 14 it puts Hg/HgO 0.927 V above RHE, in line with the 0.923 to 0.927 V labs measure. Some papers use +0.094 to +0.108 V. |
| Hg/HgO, 1 M NaOH | +0.108 V | Alkaline solutionsCalculated from activity data. Metrohm's table lists +0.140 V, which puts results about 30 mV higher. |
| Hg/Hg₂SO₄, saturated K₂SO₄ | +0.640 V | Sulfuric acid, chloride-free workSome handbooks give +0.65 V. |
| Hg/Hg₂SO₄, 0.5 M H₂SO₄ | +0.680 V | Sulfuric acid, chloride-free work |
| Reversible hydrogen (RHE) | −0.0592 × pH | Comparing results across pH |
| Standard hydrogen (SHE) | 0.000 V | The zero of the scale |
Some tables give the KCl strength per kilogram of water rather than per litre, which moves the figure by a few millivolts. Ag/Ag⁺ is left out because its potential depends on the solvent and salt.
Sources: reference electrode table (after Bard and Faulkner), silver chloride electrode, Metrohm note AN-EC-002 and a Journal of Power Sources paper on Hg/HgO in NaOH.
Frequently asked questions
How do I convert Ag/AgCl to RHE?
At 25 °C, E(RHE) = E(Ag/AgCl) + 0.197 V + 0.0592 × pH, for an Ag/AgCl electrode in saturated KCl. In 3 M KCl, use 0.210 V instead of 0.197 V.
How do I convert Hg/HgO to RHE?
At 25 °C, E(RHE) = E(Hg/HgO) + 0.098 V + 0.0592 × pH, using 0.098 V for Hg/HgO in 1 M KOH. At pH 14 the sum is E(Hg/HgO) + 0.927 V, which agrees with the 0.923 to 0.927 V labs measure when they calibrate in 1 M KOH. When the solution inside the electrode matches your electrolyte, this gap stays close to 0.927 V at any strength, because Hg/HgO and RHE both shift with the hydroxide in the same way.
Why do tables give different values for Hg/HgO?
Because they mean different things. +0.098 V is the standard potential, and most papers use it for 1 M KOH. Worked out from the real activity of hydroxide, the figure is close to +0.105 V in 1 M KOH and +0.108 V in 1 M NaOH. Metrohm's table lists +0.140 V for 1 M NaOH, which puts results about 30 mV higher. State the value you used when you report a result.
How do I convert SCE to RHE?
At 25 °C, E(RHE) = E(SCE) + 0.241 V + 0.0592 × pH.
What do I set on the potentiostat for a potential vs RHE?
Work backwards: E(set) = E(RHE) − E(reference vs SHE) − 0.0592 × pH. In the converter above, choose RHE under Measured against and your electrode under Convert to, or press Swap.
What is the difference between SHE and RHE?
The standard hydrogen electrode (SHE) is fixed at pH 0. The reversible hydrogen electrode (RHE) moves with the pH of your electrolyte, so results at different pH can be compared directly. That makes RHE the usual scale for electrocatalysis.
Are these values exact for my electrode?
No. They are published values at 25 °C, and a real electrode can differ by a few millivolts. For precise work, calibrate your reference against a reversible hydrogen electrode in your own electrolyte.
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