Basic Electrical Laws calculator

Energy Calculator

Use this energy calculator to convert watts and operating hours into kWh and estimated cost. A 1000 W load running 8 hours per day uses 8 kWh/day, 240 kWh/month, and $28.80/month at $0.12/kWh. Use the result as an energy-use screen before checking the actual tariff, demand charges, seasonal rates, or measured interval data.

Updated June 21, 2026

1000W x 8h/day x 30 days = 240 kWh/month | Cost = kWh x $/kWh

1.5kW heater 4h/day: 180 kWh/mo ≈ $21.60 @ $0.12/kWh

Enter power rating, usage hours, days, and $/kWh for a kWh and cost review

Calculator Inputs

Calculation Results

Enter values above to see calculation results

Calculation history

Example Calculations

10 hp motor running 8 hours per workday

Approximate annual energy and cost for a 7.5 kW (≈10 hp) motor operating 8 hours per day, 250 days per year at $0.12/kWh.

Inputs

Power K W: 7.5
Hours Per Day: 8
Days Per Year: 250
Rate Per K Wh: 0.12

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

Residential energy audits and bill analysis

Commercial facility energy management

Appliance energy consumption analysis

Solar system energy production calculations

Energy efficiency project evaluation

Demand charge optimization

Equipment replacement cost-benefit analysis

Environmental impact assessments

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 time (in hours): Energy (kWh) = Power (kW) × Time (hours). Power is the instantaneous rate of energy use, while energy is the total amount consumed over time. For example, a 1.5 kW appliance running for 8 hours consumes 12 kWh. Think of power as speedometer reading and energy as total distance traveled.

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.