Power Consumption Calculator

What Is Power Consumption?

Power consumption describes how fast an electrical device uses energy. When you turn on a heater, a laptop charger, an air conditioner, or a pump, the device draws electrical power from the supply. That power is measured in watts (W). Your electricity bill, however, is based on energy used over time, measured in kilowatt-hours (kWh).

The Power Consumption Calculator combines power and energy math in one place. You can calculate watts from voltage and current, convert watts to kWh over a runtime, estimate daily/monthly/yearly usage for appliances, and compute estimated cost from a per-kWh tariff.

Watts, Kilowatts, and Kilowatt-Hours

It is easy to mix up kW and kWh because they look similar. The difference is fundamental:

• W or kW is power (a rate). It tells you how fast energy is being used right now.
• kWh is energy (an amount). It tells you how much energy was used over time.

A 1 kW device running for 1 hour uses 1 kWh. The same device running for 3 hours uses 3 kWh. A smaller device, like 100 W, running for 10 hours uses 1 kWh as well (because 0.1 kW × 10 h = 1 kWh).

How to Calculate Power from Volts and Amps

For DC circuits and purely resistive AC loads (like many heating elements), power is approximately:

For many AC loads, current and voltage are not perfectly in phase. That is where power factor (PF) matters. Real power is:

In three-phase systems (common for large motors and industrial equipment), real power is:

If you do not know PF, you can use the “ignore PF” option to see apparent power (VA). But for cost and energy use, real watts are what matters because utilities bill energy based on real power consumption.

How to Calculate Energy Use (kWh)

Energy combines power and time. The most common formula for consumption is:

This is the reason small devices can still matter if they run continuously. A 10 W standby load running 24 hours a day consumes 0.24 kWh per day, which becomes 7.2 kWh per month (30 days) and 87.6 kWh per year (365 days).

Estimating Electricity Cost from Tariff

Once you know energy use, cost estimation is simple:

If your rate is 0.20 per kWh and you use 150 kWh, the energy cost is 30. Some bills add fixed fees, taxes, or tiered rates, so this calculator includes an optional fixed monthly fee and focuses on the energy-based part of your bill.

Appliance Usage: Why Real Consumption Varies

Many appliances do not run at constant power. Refrigerators cycle on and off. Air conditioners modulate with inverter drives. Computers draw different power depending on workload. Even if a label says “1500 W,” that may represent maximum draw rather than typical usage.

The appliance mode helps you estimate realistic consumption by using average hours per day and quantity. You can also add standby power for devices that stay partially on even when “off.”

Using Table Mode for Audits and Comparisons

Energy decisions are often about comparison: which device is cheaper to run, how much a runtime change affects kWh, or how much a tariff change affects cost. Table mode generates a range of scenarios and lets you export results to CSV for spreadsheets, energy audits, procurement, and reporting.

Limitations and Practical Tips

• For AC loads, use rated watts when available. Volts × amps can overestimate real power if PF is unknown or low.
• For devices with cycling or thermostats, use an estimated average power or average hours per day.
• Tariffs may include tiers, taxes, and demand charges; treat cost results as an estimate unless you model your exact billing structure.
• Three-phase calculations assume balanced load and use line voltage and line current.

Final Thoughts

Understanding power and energy is one of the simplest ways to control utility costs. When you can translate “watts” into “kWh per month” and then into cost, you can make better decisions about appliance choices, usage habits, standby power, and equipment upgrades. Use this calculator to quantify the impact of changes and build a clearer picture of your electricity consumption.