# Battery Capacity Calculator

C = I·t both ways — runtime from capacity or capacity from runtime — with optional voltage for Wh and W.

> Canonical page: https://elysiatools.com/en/tools/battery-capacity-calculator

- **Category:** Science & Education

- **Keywords:** battery capacity, battery runtime, ampere hours, mah to hours, battery life calculator, milliamp hours

## 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).

## Inputs

- **Solve for** (select)
- **Battery capacity C** (number): e.g. 4500
- **Capacity unit** (select)
- **Load current I** (number): e.g. 300
- **Current unit** (select)
- **Runtime t** (number): e.g. 48
- **Time unit** (select)
- **Nominal voltage (V, optional)** (number): e.g. 3.85

## 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

- Select the calculation mode to solve either for runtime (t = C / I) or required battery capacity (C = I · t).
- Enter the known parameters including capacity, current draw, or target runtime along with your preferred units (mAh/Ah, mA/A, min/h/d).
- Optionally enter the battery's nominal voltage to automatically calculate total energy in watt-hours (Wh) and power draw in watts (W).
- Receive 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.

## Frequently asked questions

### 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.

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