Watt-hour Calculator: Calculate Energy, Power & Time (E = P × t)

The watt-hour (Wh) is a fundamental unit of energy that represents the amount of energy consumed or produced when a power of one watt is used for one hour. Understanding watt-hours is essential for calculating energy consumption, battery capacity, and electrical costs. Our Watt-hour Calculator makes it easy to determine energy, power, or time using the simple yet powerful formula: E = P × t.

Whether you're calculating how long a battery will last, determining energy consumption of appliances, or estimating electricity costs, the watt-hour calculator simplifies these essential energy calculations.

Our Watt-hour Calculator is designed for simplicity and accuracy. Follow these steps:

1. Enter Two Values: Input any two of the three values (energy, power, or time)
2. Leave One Empty: Leave the value you want to calculate empty
3. Select Units: Choose your preferred units for each measurement
4. Click Calculate: The calculator will instantly compute the missing value with step-by-step solutions

The calculator uses the formula: E = P × t, where E is energy, P is power, and t is time.

The watt-hour formula is expressed as:

Rearranging the Formula

You can rearrange this formula to solve for any variable:

• Energy: E = P × t
• Power: P = E / t
• Time: t = E / P

Key Concepts

• Energy (E): The total amount of work done or energy consumed, measured in watt-hours (Wh) or kilowatt-hours (kWh)
• Power (P): The rate at which energy is consumed or produced, measured in watts (W) or kilowatts (kW)
• Time (t): The duration over which power is applied, measured in hours (h), minutes (min), or seconds (s)

Watt-hour calculations are used in countless real-world scenarios:

• Battery Capacity: Calculating how long batteries will last based on power consumption
• Energy Bills: Estimating electricity costs based on appliance power ratings and usage time
• Solar Power: Determining energy production from solar panels over time
• Electric Vehicles: Calculating range and charging requirements
• Home Appliances: Estimating energy consumption of refrigerators, air conditioners, and other devices
• Power Plants: Measuring energy generation and capacity
• Backup Power: Sizing UPS systems and generators for specific energy requirements
• Energy Efficiency: Comparing energy consumption of different devices and systems

Understanding energy units is crucial for accurate calculations:

• Energy Units:
  • Watt-hour (Wh): Base unit, 1 Wh = 1 W × 1 h
  • Kilowatt-hour (kWh): 1 kWh = 1,000 Wh (most common for electricity bills)
  • Megawatt-hour (MWh): 1 MWh = 1,000,000 Wh
  • Joule (J): 1 Wh = 3,600 J (SI unit of energy)
  • BTU: 1 Wh ≈ 3.412 BTU (British Thermal Unit)
• Power Units:
  • Watt (W): Base unit
  • Kilowatt (kW): 1 kW = 1,000 W
  • Megawatt (MW): 1 MW = 1,000,000 W
  • Horsepower (hp): 1 hp ≈ 745.7 W
• Time Units:
  • Hour (h): Base unit for watt-hours
  • Minute (min): 1 h = 60 min
  • Second (s): 1 h = 3,600 s
  • Day: 1 day = 24 h

Example 1: Calculating Energy Consumption

A 100 W light bulb runs for 5 hours. How much energy does it consume?

Example 2: Calculating Power from Energy

A device consumes 2.4 kWh in 8 hours. What is its power consumption?

Example 3: Calculating Time from Energy

A 50 W device has a battery capacity of 100 Wh. How long will it run?

Example 4: Monthly Energy Consumption

An air conditioner rated at 1.5 kW runs 8 hours per day for 30 days. What is the total energy consumption?

Example 5: Battery Capacity

A smartphone battery has a capacity of 3,000 mAh at 3.7 V. What is its energy capacity in Wh?

It's important to distinguish between energy and power:

• Power (W): The rate at which energy is used. It's an instantaneous measurement - like speed.
• Energy (Wh): The total amount of energy consumed over time. It's like distance traveled.

Analogy: Power is like the speed of a car (miles per hour), while energy is like the total distance traveled (miles). A high-power device uses energy quickly, while a low-power device uses energy slowly, but both can consume the same total energy over different time periods.

Watt-hour calculations are essential for understanding energy costs:

• Cost Calculation: Energy Cost = Energy (kWh) × Price per kWh
• Example: If electricity costs $0.12 per kWh and you use 500 kWh per month, your monthly cost is $60
• Energy Efficiency: Compare devices by calculating energy consumption for the same usage time
• Payback Period: Calculate how long it takes for energy-efficient devices to pay for themselves through energy savings

Understanding watt-hours and energy calculations is fundamental to managing electricity consumption, sizing batteries, and estimating costs. Our Watt-hour Calculator simplifies these calculations, making it easy to determine energy, power, or time for any electrical system.

Ready to explore more electrical concepts? Check out our other calculators like the Watt Calculator for power calculations, or the Force Calculator for mechanics calculations that often complement energy analysis.