Neutral at 25 °C — the point where hydrogen and hydroxide ion concentrations are equal, each at 10⁻⁷ mol/L. Pure water in equilibrium with air is slightly lower, around pH 5.6, because dissolved carbon dioxide forms carbonic acid.

How much more acidic is pH 4 than pH 7?

A thousand times. The scale is logarithmic, so each unit is a tenfold change: three units is 10³ = 1,000.

What is the pH of water?

Pure water is 7.0 at 25 °C, but water exposed to air settles near 5.6 as it absorbs carbon dioxide. Drinking water is normally between 6.5 and 8.5 depending on source and treatment.

Is a lower pH more acidic or more basic?

More acidic. Lower pH means higher hydrogen ion concentration. Below 7 is acidic, above 7 is basic or alkaline.

What is the pH of bleach?

Household bleach is typically around pH 12.5 to 13 — strongly basic. Drain cleaner at pH 14 is more so. Both are corrosive to skin and eyes, and bleach in particular must not be mixed with acids.

Yes. The scale is not bounded at 0 — concentrated hydrochloric acid has a negative pH. The 0–14 range is a convention for dilute aqueous solutions, not a limit of the definition.

pH Scale Chart

The pH scale from 0 to 14 with common substances, the hydrogen ion concentration at each value, and a representative acid or base.

Page last changed 2026-10-19 · based on n/a — definition is stable; example values are approximate

Quick Answer

pH is a logarithmic scale of hydrogen ion concentration: pH = −log₁₀[H⁺]. Each whole step is a tenfold change, so pH 4 is 1,000 times more acidic than pH 7. Below 7 is acidic, above 7 is basic, and 7 is neutral at 25 °C.

Find a value

pH Values of Common Substances

pH^[2]	Example^[2]	H⁺ concentration mol/L^[1]	Typical acid or base^[2]
0 #	Battery acid	1,000,000	Hydrochloric acid
1 #	Stomach acid, gastric	100,000	Sulphuric acid 0.1 N
2 #	Lemon juice, vinegar	10,000	Citric acid
3 #	Orange juice, soda	1,000	Acetic acid
4 #	Tomato juice, beer	100	Lactic acid
5 #	Black coffee, bananas	10	Boric acid
6 #	Milk, urine	1	Carbonic acid
7 #	Pure water	0.0000001	Neutral
8 #	Sea water, baking soda	0.000001	Sodium bicarbonate
9 #	Baking soda solution	0.00001	Borax
10 #	Milk of magnesia	0.0001	Magnesium hydroxide
11 #	Ammonia solution	0.001	Ammonium hydroxide
12 #	Soapy water, lime	0.01	Calcium hydroxide
13 #	Bleach, oven cleaner	0.1	Sodium hydroxide
14 #	Drain cleaner	1	Sodium hydroxide conc.

pH values are approximate and depend on concentration and temperature. The H⁺ concentration column is the exact value at each whole pH unit, computed as 10⁻ᵖᴴ — the scale is logarithmic, so it changes by a factor of ten per unit.

The Logarithmic Scale

pH = −log₁₀[H⁺]
[H⁺] = 10⁻ᵖᴴ mol/L

Because the scale is logarithmic, differences that look small are not. The gap between pH 3 and pH 6 is a thousandfold change in acidity, not a doubling. This is why diluting an acid by a factor of ten moves the pH by exactly one unit.

The scale runs 0–14 for practical purposes in water at 25 °C, but it is not bounded: concentrated strong acids have negative pH, and concentrated bases exceed 14.

What Sets the Neutral Point

pH 7 is neutral at 25 °C because that is where the self-ionisation of water gives equal concentrations of H⁺ and OH⁻, each at 10⁻⁷ mol/L. The neutral point is temperature-dependent: at 100 °C it falls to about pH 6.14, and at 0 °C it rises to about 7.47.

This matters in practice for boiler water and high-temperature process chemistry, where "neutral" is not 7. It is also why pH measurements are always reported with a temperature.

Frequently Asked Questions

What is pH 7?: Neutral at 25 °C — the point where hydrogen and hydroxide ion concentrations are equal, each at 10⁻⁷ mol/L. Pure water in equilibrium with air is slightly lower, around pH 5.6, because dissolved carbon dioxide forms carbonic acid.
How much more acidic is pH 4 than pH 7?: A thousand times. The scale is logarithmic, so each unit is a tenfold change: three units is 10³ = 1,000.
What is the pH of water?: Pure water is 7.0 at 25 °C, but water exposed to air settles near 5.6 as it absorbs carbon dioxide. Drinking water is normally between 6.5 and 8.5 depending on source and treatment.
Is a lower pH more acidic or more basic?: More acidic. Lower pH means higher hydrogen ion concentration. Below 7 is acidic, above 7 is basic or alkaline.
What is the pH of bleach?: Household bleach is typically around pH 12.5 to 13 — strongly basic. Drain cleaner at pH 14 is more so. Both are corrosive to skin and eyes, and bleach in particular must not be mixed with acids.
Can pH be negative?: Yes. The scale is not bounded at 0 — concentrated hydrochloric acid has a negative pH. The 0–14 range is a convention for dilute aqueous solutions, not a limit of the definition.

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

#	Source	Type	Revision / method
[1]	Hydrogen ion concentration	derived	[H⁺] = 10⁻ᵖᴴ mol/L, computed exactly at each whole pH unit.
[2]	pH scale definition with typical values for common substances	reference	n/a — the definition is fixed; example values are approximate — source

Data Sources

Standard	Revision	What it covers on this page
IUPAC definition of pH	n/a — definition is stable; example values are approximate	the scale definition and the H⁺ concentration column

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
H⁺ concentration	10⁻ᵖᴴ mol/L.

Example pH values are approximate and depend on concentration and temperature. The H⁺ column is exact at each whole pH unit.

Accuracy and use. Use the source notes and recorded verification scope above to assess each value. Calculated values follow the stated derivations; compilation values may lack a confirmed original document or product condition. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Read the source notes, calculation methods and verification scope above before reusing a value. To cite this page:

Plain text

Engineering Reference. "pH Scale Chart." https://refmanual.com/charts/ph-scale/ (accessed 2026-10-19). Data from IUPAC definition of pH, n/a — definition is stable; example values are approximate.

BibTeX

@misc{ph-scale,
  title        = {pH Scale Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/ph-scale/}},
  note         = {Accessed: 2026-10-19},
  source       = {IUPAC definition of pH, n/a — definition is stable; example values are approximate}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - pH Scale Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/ph-scale/
PY  - 2026
DA  - 2026-10-19
N1  - Source: IUPAC definition of pH, n/a — definition is stable; example values are approximate
ER  -

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