Basic Electrical Laws calculator
Energy Calculator
Use this energy calculator to enter watts or kW, operating hours, billing days, and $/kWh rate before converting a load profile into daily, monthly, and annual kWh and cost. Use measured watts where possible, then compare the result against the actual tariff, demand charges, seasonal rates, or measured interval data.
Updated July 16, 2026
Enter watts or kW, operating hours, billing days, and $/kWh to calculate kWh use and cost.
Use measured watts or nameplate kW, then compare daily, monthly, and annual energy cost.
Enter power rating, usage hours, days, and $/kWh for a kWh and cost review
Example Calculations
How to Use
How this energy calculator models kWh and cost
This tool applies the standard relationship Energy (kWh) = Power (kW) × Time (hours) and then multiplies by your tariff rate to estimate cost. It is designed for engineers, technicians, and facility staff who have either nameplate data or measured power from meters, data loggers, or BMS systems.
Typical questions this calculator answers:
- How many kWh does a specific load or group of loads use per day, month, or year?
- What is the approximate cost impact of adding or removing a load?
- How does an efficiency upgrade change annual kWh and operating cost?
Core formulas used
- Power (kW) = Power (W) ÷ 1000
- Energy (kWh) = Power (kW) × Time (hours)
- Cost = Energy (kWh) × Rate ($/kWh)
- When only current is known, approximate power with kW ≈ V × I × PF ÷ 1000
For more detailed power and power factor work, use the power calculator. To include transformer and distribution losses explicitly, combine this calculator with the transformer calculator and, where motors dominate, the motor current calculator.
What you are actually estimating
| Calculation type | What it tells you | Typical use | Technical caveats |
|---|---|---|---|
| Energy consumption | Total kWh over a defined window | Monthly bill estimates, feeder loading checks | Does not include explicit demand charges or power-factor penalties |
| Energy comparison | Difference in kWh and cost between two options | LED retrofits, motor replacements, HVAC upgrades | Payback ignores maintenance savings and incentives unless you model them separately |
| Solar energy offset | kWh produced and net kWh imported from the grid | Solar system sizing, net-metering analysis | Weather, soiling, and inverter efficiency reduce output from nameplate values |
| Demand window analysis | Average kW over utility billing intervals | Commercial demand billing and load management | Many utilities use 15- or 30-minute windows; short spikes can dominate demand charges |
Common calculation scenarios
| Scenario | Key inputs | What to watch | Typical range |
|---|---|---|---|
| Office equipment audit | Device power, diversity factor, run hours | Sleep-mode power, plug strips, phantom loads | Tens to low hundreds of kWh per workstation per year |
| HVAC system analysis | Tonnage, COP/SEER, operating hours, climate | Part-load efficiency, duct and distribution losses | Often the largest single contributor to annual kWh in commercial buildings |
| Industrial motor evaluation | HP rating, load factor, run hours, power factor | Starting method, demand charges, power-factor penalties | Hundreds to tens of thousands of kWh per motor per year |
| Solar system sizing | Array kW, sun hours, inverter and system efficiency | Shading, temperature derating, clipping at inverters | Roughly 1,200-1,800 kWh/year per kW installed depending on site |
For cost analysis, combine kWh results from this calculator with the electricity cost calculator to break out energy and demand components on the bill. Use measured data from quality meters wherever possible; nameplate values are only an approximation of real operating conditions.
Understanding the relationship between power and energy starts with the fundamentals; see the Power Formulas Guide for P = V × I, P = I²R, and three-phase formulas. To calculate electricity costs from energy usage, try the Electricity Cost Calculator.
Common Applications
More applications. Open to review 5 additional use cases.
Frequently Asked Questions
How do I calculate energy consumption and understand the difference between energy and power?
Energy consumption in kWh is calculated by multiplying power in kilowatts by operating time in hours. Power is the instantaneous rate of energy use, while energy is the total amount consumed over time. Enter the equipment power, run time, and billing period in the calculator to get the project-specific kWh result.
What factors affect my electricity bill and how can I reduce costs?
Electricity bills include energy consumption (kWh), electricity rates ($/kWh), demand charges for peak usage, time-of-use rates, connection fees, and taxes. Commercial customers may face power factor charges. Reduce costs by using energy-efficient equipment, implementing proper controls and scheduling, improving power factor, reducing peak demand, and considering renewable energy sources. The calculator helps evaluate cost-effectiveness of efficiency improvements.
How do demand charges work and why are they important for commercial facilities?
Demand charges are based on your highest power usage during peak periods, typically measured in 15-minute intervals. In many commercial tariffs they account for a significant share of the total bill. Utilities apply demand charges because they must maintain capacity to meet peak loads. Reduce demand charges through load scheduling, energy storage, power factor correction, and demand response programs. The calculator helps you compare kWh and kW patterns when evaluating reduction strategies.
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