Watts measure power, indicating the rate of energy transfer or conversion. Named after Scottish inventor James Watt, this unit is vital in fields like electrical engineering and physics. Understanding watts helps you evaluate an electrical device’s performance by gauging its energy consumption and efficiency.

## What Are Watts In Simple Terms?

A watt measures the rate of electricity usage or production.

Think of it like filling a bucket with water: the flow rate represents power, similar to how watts function for electricity.

For instance, a 60-watt light bulb consumes 60 watts of of electricity at any given moment when on; higher wattage means greater energy consumption.

## Common Watt Multiples and What They Mean

Watts are evaluated in multiples of 1,000.

- The milliwatt (1/1000th of a watt) is the smallest unit, commonly used to measure the output power of LEDs and lasers.

- A kilowatt (kW) equals 1,000 watts and is a standard unit for measuring electricity; your electric bill likely reflects this measurement.
- A megawatt (MW) equals 1,000 kilowatts, used to measure the power of large electric motors, submarines, and aircraft carriers.
- One gigawatt (GW) equals one billion watts, typically used to measure the output power of large electric generators. Large cities may consume this amount of wattage instantly.

Electric devices at home are rated in watts or kilowatts; for example, a light bulb may use 60 watts while a microwave uses 750 watts.

Appliances like refrigerators have different ratings: a start rating (e.g., 1,200 watts) when first turned on and a running capacity (e.g., 800 watts) during normal operation, which can be a bit confusing.

## How to Measure Watts?

To measure watts, you need to know the amps and volts from a power source, which can be measured with a multimeter.

For DC circuits, use the equation: Watts (W) = Volts (V) × Amperes (A).

For example, a device operating at 120 volts and drawing 2 amperes consumes power as follows: W = 120 V × 2 A = 240 W.

This can also be expressed as Power = Amps x Volts (P = I*V) in more technical contexts.

In AC power measurement, the power factor (PF) adds complexity since watts = volts x amps x PF. The power factor measures how effectively an electrical device converts volt-amperes into watts.

## High Wattage vs Low Wattage

High wattage means higher power consumption, prompting the creation of lower-wattage appliances.

However, high wattages are beneficial for generating heat; hotter heaters have higher wattage.

It’s important to note that high-wattage appliances produce more heat and can overload circuits, leading to blown fuses or tripped breakers.

In contrast, low-wattage devices like cell phone chargers and LED bulbs require less power.

## Difference Between Watts & Watt-Hours

Watts measure the power a device uses, while watt-hours measure the energy consumed over time.

One watt-hour equals one watt used for an hour.

For example, a 10-watt LED bulb left on for one hour consumes 10 watt-hours of energy.

## Power Supply Capacity

A power supply’s capacity, measured in wattage, indicates the maximum power it can deliver.

When selecting a power supply, choose one with sufficient wattage for your system’s needs.

It’s better to have excess capacity than insufficient power. Aim for 10–20% headroom between the power supply’s maximum rating and your system’s requirements.

For instance, if a device needs 200 watts, don’t use a 200-watt power supply; choose one with higher wattage, like a 240-watt power supply.

## Why Do Watts Matter in RVs & Boats?

When traveling in an RV or boat, calculating your daily power requirements is crucial.

For marine applications, understand the necessary motor power based on your boat’s size.

In RVs, determine which appliances you can run simultaneously.

For instance, a generator providing 4,000 watts can support an air conditioner, microwave, and several small appliances but not all at once.

If considering a solar system for your boat or RV, calculate your 24-hour wattage to determine how many solar panels you need based on their wattage to sustain daily usage.

## How Many Watts of Solar Do You Need?

To determine the wattage needed for solar panels to power the RV, boat or off-grid, start by listing all electrical devices will be used. Record each device’s wattage and intended running time.

Next, add the wattages together and total the running times. Multiply these two totals (total wattage x total projected running time) to find the required watt-hours.

For example, if you plan to run all devices for 12 hours with a 250-watt solar panel, it can produce 3,000 watt-hours (250 x 12 = 3,000). If your total requirement exceeds 3,000 watt-hours over that period, you’ll need more than one panel.

This method is simplified; many other factors will affect solar needs. For a more detailed approach to calculating requirements for an RV, you can check etrailer’s article.