C = I·t both ways — runtime from capacity or capacity from runtime — with optional voltage for Wh and W.
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Tool usage guide
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Key facts
Category
Science & Education
Input types
select, number
Output type
text
Sample coverage
4
API ready
Yes
Overview
The Battery Capacity Calculator solves the fundamental battery relationship C = I·t in both directions, computing operating runtime from known capacity and load or calculating required capacity to sustain a specific runtime. It supports standard capacity units (mAh, Ah), current draws (mA, A), and timeframes (minutes, hours, days), with optional nominal voltage input to compute total energy in watt-hours (Wh) and average power draw in watts (W).
When to use
Estimating how long a portable device or battery pack will run under a known average current draw.
Sizing the required battery capacity in mAh or Ah for an IoT device, sensor, or microcontroller project targeting a specific operating lifespan.
Converting battery capacity and nominal voltage into watt-hours (Wh) and average power consumption in watts (W).
How it works
1Select the calculation mode to solve either for runtime (t = C / I) or required battery capacity (C = I · t).
2Enter the known parameters including capacity, current draw, or target runtime along with your preferred units (mAh/Ah, mA/A, min/h/d).
3Optionally enter the battery's nominal voltage to automatically calculate total energy in watt-hours (Wh) and power draw in watts (W).
4Receive instant, formatted results detailing runtime, required capacity, and electrical energy metrics.
Use cases
Electronics hobbyists sizing lithium-ion or LiPo batteries for DIY Arduino and ESP32 projects.
Embedded hardware engineers calculating battery life requirements for remote sensors and IoT nodes.
Field technicians assessing the expected runtime of portable instruments and backup power packs.
Examples
1. Estimating Smartphone Runtime Under Typical Load
Hardware Reviewer
Background
A reviewer wants to verify the theoretical active screen-on runtime of a mobile phone based on its specified battery pack.
Problem
Determine how many hours a 4500 mAh battery lasts under an average system draw of 300 mA at 3.85 V nominal voltage.
How to use
Set mode to 'Runtime from capacity', enter 4500 mAh for capacity, 300 mA for current, and 3.85 V for nominal voltage.
Outcome
Calculates an expected runtime of 15 hours, yielding 17.325 Wh total energy and an average power draw of 1.155 W.
2. Sizing an IoT Soil Moisture Sensor Battery
IoT Developer
Background
An engineer is deploying an off-grid agricultural sensor node that draws an average of 5 mA and must operate unattended for 30 days.
Problem
Calculate the total battery capacity in mAh and Ah needed to sustain the device for the full 30-day period using a 3.6 V cell.
How to use
Set mode to 'Capacity needed for runtime', enter 5 mA for current, 30 d for runtime, and 3.6 V for nominal voltage.
Outcome
FAQ
What formula does this calculator use?
It uses the linear battery equation C = I · t, where C is capacity, I is average current, and t is time, along with P = V · I and E = V · C when nominal voltage is provided.
How do I convert mAh to watt-hours (Wh)?
Multiply the capacity in milliampere-hours by the nominal voltage in volts and divide by 1,000: Wh = (mAh × V) / 1000.
Does this tool account for Peukert's law or discharge efficiency?
No, this calculator provides theoretical baseline values based on ideal linear discharge without Peukert derating or ambient temperature losses.
Which units are supported for capacity and current?
You can select milliampere-hours (mAh) or ampere-hours (Ah) for capacity, and milliamperes (mA) or amperes (A) for current.
Is entering nominal voltage required?
No, nominal voltage is optional. If left blank, the tool calculates runtime or capacity without watt-hour and watt energy metrics.