Battery C-Rate Calculator
Calculate the C-rate associated with a current and a stated amp-hour capacity, along with an idealized capacity/current duration.
How to use this calculator
- Enter rated capacity (ah), charge or discharge current (a); check the units and use values from the same period or scenario.
- Review the result and intermediate values; change one input at a time when comparing scenarios.
- Keep the stated formula and assumptions with any result you share.
Formula and method
C-rate = current in amperes ÷ capacity in amp-hours. Ideal duration at that current = capacity ÷ current hours.
- The current is 0.25C, corresponding to an idealized 4-hour capacity/current ratio.
- Actual usable capacity and safe current depend on chemistry, temperature, age, voltage cutoffs and the manufacturer’s limits.
Worked examples
Worked example
A 100 Ah battery supplies 25 A.
The current is 0.25C, corresponding to an idealized 4-hour capacity/current ratio.
The current is 0.25C, corresponding to an idealized 4-hour capacity/current ratio.
Understanding the result
The current is 0.25C, corresponding to an idealized 4-hour capacity/current ratio.
Actual usable capacity and safe current depend on chemistry, temperature, age, voltage cutoffs and the manufacturer’s limits.
Important notes
Actual usable capacity and safe current depend on chemistry, temperature, age, voltage cutoffs and the manufacturer’s limits.
Use measured inputs and verify that the model matches the situation before making an operational, financial or technical decision.
Frequently asked questions
Does 1C always mean one hour of runtime?
It is a nominal ratio; real usable duration depends on the battery and discharge conditions.
Can I use this to set a safe charge current?
Use the battery datasheet and battery-management limits, not this calculation alone.
What should I check before relying on this result?
Verify units, input definitions and assumptions against your real data or the relevant product, service or professional guidance.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.