What is the formula for pH?

The formula is `pH = -log₁₀[H⁺]`, where [H⁺] is the molar concentration of hydrogen ions in moles per liter.

What is the relationship between pH and pOH at 25°C?

At 25°C (standard laboratory temperature), `pH + pOH = 14.0` because the autoionization constant of water is $K_w = 1.0 \times 10^{-14}$.

How do you calculate [H+] from a pH of 3.5?

`[H⁺] = 10^(-3.5) = 3.16 × 10^-4 mol/L` (or 0.000316 M).

Can pH be negative or greater than 14?

Yes, extremely concentrated strong acids (e.g., 12M HCl) can have negative pH (pH ≈ -1.08), and concentrated strong bases (e.g., 10M NaOH) can have pH > 14.

What are common real-world pH values?

Battery acid is pH ~0.5, lemon juice pH ~2.2, coffee pH ~5.0, pure water pH 7.0, human blood pH 7.35–7.45, bleach pH ~12.5.

How is solution pH calculated from hydrogen ion concentration [H+]?

pH is the negative logarithm of hydrogen ion activity: `pH = -log10[H+]`. Neutral pure water at 25°C has a pH of 7.0.

Science & Engineering Cluster

pH Calculator (Acidity, Alkalinity, [H+] & pOH)

Calculate pH, pOH, hydrogen ion concentration, and hydroxide ion concentration for aqueous solutions.

TL;DR: pH Calculator evaluates aqueous acidity and alkalinity, calculating pH = -log10[H+], pOH = -log10[OH-], and ion concentrations at standard 25°C.

Calculate from

pH value

How Do You Calculate pH from Hydrogen Ion Concentration [H+]?

pH is calculated using the negative base-10 logarithm of hydrogen/hydronium ion molarity: pH = -log₁₀[H⁺]. Conversely, [H⁺] = 10^(-pH). At 25°C in pure water, pH + pOH = 14.0, allowing pOH and [OH⁻] to be determined directly: pOH = 14 - pH and [OH⁻] = 10^(-pOH).

How to Use the pH Calculator

Our pH Calculator performs high-precision mathematical operations directly in your browser with zero latency and complete client-side privacy.

Select your known input parameter: pH, pOH, $[\text{H}^+]$ concentration, or $[\text{OH}^-]$ concentration.
Enter the numerical value (supports scientific notation such as `1.5e-4`).
Click 'Calculate' to see instant logarithmic acidity values.
Review the acid/base classification scale (Acidic < 7, Neutral = 7, Alkaline/Basic > 7).
Copy the electrochemical values for water treatment, aquariums, or chemistry labs.

Mathematical Formula & Equations

Calculates acidity and alkalinity from hydrogen ion concentration $[\text{H}^+]$.

\[ \text{pH} = -\log_{10}[\text{H}^+], \quad \text{pOH} = -\log_{10}[\text{OH}^-], \quad \text{pH} + \text{pOH} = 14 \]

Calculation Example

For a solution with $[\text{H}^+] = 1.0 \times 10^{-4}\text{ M}$: $$\text{pH} = -\log_{10}(10^{-4}) = 4.0 \text{ (Acidic)}$$

100% Client-Side Privacy & Data Security

All calculations, amortization schedules, variables, and sensitive numerical datasets execute 100% locally in your web browser memory. Your financial, medical, and personal values are never transmitted, logged, or uploaded to any external server.

Frequently Asked Questions

: The formula is `pH = -log₁₀[H⁺]`, where [H⁺] is the molar concentration of hydrogen ions in moles per liter.
: At 25°C (standard laboratory temperature), `pH + pOH = 14.0` because the autoionization constant of water is $K_w = 1.0 \times 10^{-14}$.
: `[H⁺] = 10^(-3.5) = 3.16 × 10^-4 mol/L` (or 0.000316 M).
: Yes, extremely concentrated strong acids (e.g., 12M HCl) can have negative pH (pH ≈ -1.08), and concentrated strong bases (e.g., 10M NaOH) can have pH > 14.
: Battery acid is pH ~0.5, lemon juice pH ~2.2, coffee pH ~5.0, pure water pH 7.0, human blood pH 7.35–7.45, bleach pH ~12.5.
: pH is the negative logarithm of hydrogen ion activity: `pH = -log10[H+]`. Neutral pure water at 25°C has a pH of 7.0.

Cite This Calculator

Need to reference this online calculator in a financial proposal, academic paper, blog post, or classroom curriculum? Copy a citation below.

NexLove.org. (2026). pH Calculator [Online Calculation Tool]. https://nexlove.org/tools/ph-calculator

“pH Calculator.” NexLove.org, 2026, nexlove.org/tools/ph-calculator.

NexLove.org (2026) pH Calculator. Available at: https://nexlove.org/tools/ph-calculator (Accessed: 2026).

@misc{nexlove_ph_calculator,
  title = {pH Calculator},
  author = {{NexLove.org}},
  year = {2026},
  url = {https://nexlove.org/tools/ph-calculator}
}

Embed This Tool

Add the live pH Calculator to your own website with this snippet — it loads the real, working calculator in an iframe.

<iframe src="https://nexlove.org/embed/ph-calculator.html" width="100%" height="600" style="border:1px solid #e2e8f0;border-radius:12px" title="pH Calculator — NexLove.org" loading="lazy"></iframe>

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