pKa Calculator
Chemistry
Calculate pka with explicit inputs and a worked example.
Formula
pKa = −log₁₀(Ka)
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Educational calculation using the stated ideal model. Inputs must describe the same system; not a dosing or laboratory procedure.
Example Calculation
Example inputs
- Acid dissociation constant Ka: 0.00001
Ka = 10⁻⁵ gives pKa = 5.
Frequently asked questions
How do I use this calculator?
Enter acid dissociation constant ka. The result updates automatically. Use Reset to restore the example values.
What method does it use?
pKa = −log₁₀(Ka). Educational calculation using the stated ideal model. Inputs must describe the same system; not a dosing or laboratory procedure.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.