H+ to pH & pH to H+ Converter
Convert hydrogen ion concentration [H+] to pH, convert pH back to [H+] in your chosen unit, or compare two pH values to see exactly how many times more acidic one solution is than another — with full step-by-step working.
Pick a direction, then enter your value.
pH value
Formula used: pH = -log10[H+]
6
pH value
1.000 x 10^-6 M
[H+] concentration
1.000 x 10^-8 M
[OH-] concentration
8
pOH value
Interactive pH Scale
See exactly where each value sits on the 0–14 pH scale, next to everyday substances.
Step-by-Step Conversion
Here's exactly how this answer was calculated, one step at a time.
Given: [H+] = 1 µmol/L
Step 1: Convert the input into mol/L
The pH formula only works with concentration in moles per litre, so any other unit is converted first.
[H+] = 1 µmol/L = 1.000 x 10⁻⁶ mol/LStep 2: Apply the pH formula
pH = -log10[H+] = -log10(1.000 x 10⁻⁶)Step 3: Result
pH = 6
Calculated pH:
6
H+ to pH & pH to H+ Converter: Convert Hydrogen Ion Concentration in Seconds
This free H+ to pH converter is built for chemistry students, lab technicians, water-quality staff, aquarium and hydroponics hobbyists, and anyone who needs to move quickly between hydrogen ion concentration and pH. It handles three common situations: converting a measured [H+] concentration into pH, converting a known pH back into [H+] in the unit you actually work with (mol/L, mmol/L, µmol/L or nmol/L), and comparing two pH values to see exactly how many times more acidic one solution is than another.
Every result shows pH alongside the matching pOH, [H+] and [OH-] concentrations, a plain-language classification of how acidic or basic the solution is, an interactive pH scale, and a complete written solution so you can follow exactly how the answer was reached. Pick the conversion that matches the information you already have, type in your numbers, and the result appears instantly with no sign-up and no software to install.
What Is Hydrogen Ion Concentration [H+]?
Hydrogen ion concentration, written [H+], measures how many hydrogen ions (also called protons or hydronium ions, H3O+) are dissolved in one litre of a water-based solution. It is normally expressed in moles per litre (mol/L), but in real lab work the numbers involved are often extremely small, so chemists frequently report [H+] in millimoles per litre (mmol/L), micromoles per litre (µmol/L), or even nanomoles per litre (nmol/L) instead of writing out a long decimal.
Because [H+] directly drives every acid-base property of a solution, it is the single most important number behind pH. A higher [H+] means a more acidic solution, and a lower [H+] means a more basic (alkaline) one. This converter accepts [H+] in any of those four common units and automatically standardises the value to mol/L before applying the pH formula, so you never need to do the unit math by hand.
The pH Formula: pH = -log10[H+]
The formula behind every H+ to pH conversion is pH = -log10[H+], where [H+] is the hydrogen ion concentration in moles per litre. Because raw concentrations are awkward tiny decimals like 0.0001 or 0.00000025, taking the negative base-10 logarithm compresses them into a clean, easy-to-compare number on the familiar 0–14 pH scale.
For example, if [H+] = 1 x 10^-4 mol/L, the pH is -log10(0.0001), which equals 4. A smaller, more negative exponent in the concentration (meaning more hydrogen ions present) always gives a lower pH, while fewer hydrogen ions push the pH higher. This converter performs that calculation instantly the moment you enter a concentration, no matter which unit you choose.
Converting pH Back to [H+]: [H+] = 10^(-pH)
Going the other direction — from a known pH back to hydrogen ion concentration — simply reverses the logarithm: [H+] = 10^(-pH). This is the calculation most often needed when a pH meter, a lab report, or a textbook problem gives you a pH value and you actually need the underlying molarity for a dilution, a titration, or a kinetics calculation.
For instance, a solution with pH 5 has [H+] = 10^-5 mol/L, or 0.00001 mol/L. Expressed in more lab-friendly units, that is the same as 10 µmol/L, which is often the more natural way to describe it when you are pipetting small volumes. This converter shows the answer in mol/L and instantly re-expresses it in mmol/L, µmol/L or nmol/L, whichever you select.
Why Concentration Units Matter: mol/L, mmol/L, µmol/L and nmol/L
Hydrogen ion concentrations shrink fast as pH rises: a pH 3 solution has [H+] around 1 mmol/L, a pH 6 solution sits near 1 µmol/L, and a pH 9 solution is down around 1 nmol/L. Writing all of these in mol/L means constantly juggling negative exponents, which is exactly where unit conversion mistakes creep in.
This converter lets you enter or read out [H+] directly in mol/L, mmol/L, µmol/L or nmol/L, matching whichever unit your instrument, protocol, or textbook uses. Internally, every value is standardised to mol/L before the pH formula is applied, so switching units never changes the underlying chemistry — only how the number is displayed.
Acidity Ratio: How Many Times More Acidic Is One Solution Than Another?
Because pH is logarithmic, a difference of just one whole pH unit represents a 10-fold change in hydrogen ion concentration, and a difference of two units represents a 100-fold change. This is easy to state but genuinely hard to picture without doing the exponent math yourself, which is exactly what the built-in acidity ratio tool handles for you.
Enter the pH of two solutions and this converter calculates the exact ratio [H+]A / [H+]B = 10^(pHB - pHA), tells you which solution is more acidic, and states the fold-difference in plain language. For example, comparing lemon juice at pH 2.2 with black coffee at pH 5 shows the lemon juice carries roughly 630 times more hydrogen ions — a far more intuitive way to understand acidity than comparing the pH numbers alone.
Worked Examples for Common Substances
Stomach acid sits around pH 1.5, meaning [H+] is roughly 0.032 mol/L, or 32 mmol/L — an extremely concentrated hydrogen ion environment built for digesting food. Black coffee, by contrast, has a pH near 5, putting [H+] at about 10 µmol/L, thousands of times more dilute than stomach acid despite both being called 'acidic'.
Pure water at pH 7 has [H+] = 1 x 10^-7 mol/L, or 100 nmol/L, exactly balanced against an equal [OH-]. Household ammonia, around pH 11.5, has [H+] of just about 3 nanomoles per litre — vanishingly small compared with stomach acid, which is precisely why the negative logarithm scale exists: it turns a range spanning fourteen powers of ten into numbers you can actually compare at a glance.
How pH, pOH, [H+] and [OH-] All Connect
In any aqueous solution at 25 degrees Celsius, hydrogen and hydroxide ion concentrations are linked by the water dissociation constant Kw, where [H+] multiplied by [OH-] always equals 1.0 x 10^-14. Taking the negative logarithm of that relationship gives the well-known shortcut pH + pOH = 14, which this converter applies automatically alongside every [H+]-to-pH conversion.
That means every result here also shows you the matching pOH and [OH-] concentration for free, without needing to run a separate calculation. If you specifically need to work from a hydroxide concentration instead, the companion pOH Calculator on this site covers that direction directly, including strong base, weak base, and buffer scenarios.
Common Mistakes to Avoid When Converting Between pH and [H+]
A frequent mistake is forgetting the negative sign in pH = -log10[H+], which turns a correctly acidic result into a confusing negative pH. Another common slip is mixing up units — entering a value in µmol/L while assuming it is in mol/L overstates the concentration by a factor of a million and produces a pH that is off by roughly six whole units.
It is also easy to forget that pH changes are exponential, not linear: assuming a pH drop from 6 to 5 represents 'twice as much acid' badly understates the real 10-fold increase in [H+]. When in doubt, use the acidity ratio tool above rather than estimating fold-differences by eye, and always double-check which concentration unit your source data is actually reported in before typing it in.
Why This Conversion Matters in Real Work
Outside the classroom, converting cleanly between pH and [H+] matters anywhere acid strength needs to be quantified rather than just read off a meter. Analytical chemists convert pH meter readings back into [H+] for kinetics calculations and rate-law work, since reaction rates depend on actual concentration, not the compressed pH number. Water treatment and environmental labs report drinking water and effluent limits in both pH and equivalent hydrogen ion concentration for regulatory paperwork.
In biology and medicine, blood pH of 7.35–7.45 corresponds to an extremely narrow [H+] window of roughly 35–45 nmol/L, and clinicians sometimes reason in nanomolar hydrogen ion terms specifically because it makes small, dangerous shifts easier to spot than the compressed pH scale does. Aquarium keepers, hydroponics growers, and food scientists also lean on quick pH-to-concentration conversions when dosing pH-adjusting solutions, where knowing the actual fold-change in acidity avoids over- or under-correcting.
Using This Converter Alongside a pH Meter or Lab Titration
A calibrated pH meter reports pH directly, but the underlying electrode is actually responding to hydrogen ion activity in solution, so it is often useful to see what concentration that reading actually represents. Typing a meter reading straight into the pH-to-[H+] mode instantly shows the equivalent molarity, which is the number you actually need for stoichiometry, dosing calculations, or comparing against a known standard curve.
During an acid-base titration, [H+] changes by orders of magnitude near the equivalence point even though the pH meter display only moves by a few units, which is exactly why titration curves look so steep there. Converting a handful of pH readings taken during a titration into [H+] with this tool makes it easy to see how sharply the hydrogen ion concentration is actually collapsing, well before it would be obvious from the pH numbers alone.
H+ to pH Converter: Quick Reference Summary
Use pH = -log10[H+] whenever hydrogen ion concentration is known, remembering to convert mmol/L, µmol/L or nmol/L into mol/L first (or let this converter do it automatically). Use [H+] = 10^(-pH) whenever only pH is available, and re-express the result in whichever concentration unit your work requires. Remember that pH + pOH = 14 at 25 degrees Celsius, so both values are always available from a single input.
To compare acidity between two solutions, do not compare raw pH numbers directly — use the ratio tool, since every whole pH unit apart means a 10x difference in [H+]. This free converter is intended to support learning, lab planning, and everyday chemistry questions. For safety-critical, regulated, clinical, or industrial work, always confirm results with validated lab instruments and your organisation's approved procedures.
Frequently Asked Questions
How do I convert [H+] to pH?
Use pH = -log10[H+], with [H+] expressed in moles per litre (mol/L). If your concentration is in mmol/L, µmol/L or nmol/L, convert it to mol/L first — this converter does that automatically.
How do I convert pH to [H+]?
Use [H+] = 10^(-pH). The result comes out in mol/L by default; this converter can also display it directly in mmol/L, µmol/L or nmol/L.
What is [H+] in mol/L for pH 7?
At pH 7, [H+] = 10^-7 mol/L, which equals 100 nmol/L. This is the neutral point of the pH scale at 25 degrees Celsius.
How many times more acidic is pH 3 than pH 5?
Exactly 100 times more acidic. Each whole pH unit represents a 10-fold change in [H+], so a two-unit gap (pH 3 vs pH 5) equals a 10 x 10 = 100-fold difference in hydrogen ion concentration.
Why does a lower pH mean a higher [H+] concentration?
Because pH is defined as the negative logarithm of [H+]. As hydrogen ion concentration increases, its negative logarithm decreases, so a more acidic solution (more H+ ions) always has a lower pH number.
What is the difference between [H+] and pH?
[H+] is the actual hydrogen ion concentration in moles per litre — a raw chemical quantity. pH is a compressed, logarithmic scale built from [H+] specifically to make that huge range of concentrations easy to read and compare.
How do I convert [H+] in µmol/L to pH?
Multiply the µmol/L value by 1 x 10^-6 to get mol/L, then apply pH = -log10[H+]. This converter performs that conversion automatically when you select µmol/L as your input unit.
Can this converter compare the acidity of two different pH values?
Yes. Choose the acidity ratio mode, enter both pH values, and the converter calculates the exact fold-difference in [H+] between them and states which solution is more acidic.