Electricity Calculator

An electricity calculator works in two modes. Electricity Cost mode estimates energy consumption and expense for any electrical device over a specified period. Ohm's Law mode solves for an unknown electrical value, voltage, current, resistance, or power, from two known values.

Device wattage is the power rating of the appliance, found on the device label, in the product manual, or on the manufacturer website. Common examples: an LED bulb at 10 W, a laptop at 65 W, a space heater at 1500 W, and a window air conditioner at 1200 W. Hours used per day reflects typical daily usage and accepts fractional and mixed numbers such as 6.5 or 6 1/2. Number of days matches a billing cycle or a desired calculation period; a typical monthly billing cycle is 30 days. Electricity rate, per kWh, comes from a utility bill; in the United States the average residential rate runs approximately $0.12 to $0.16 per kilowatt-hour, and a recent bill gives the exact figure. Results report energy consumed in kilowatt-hours, cost for the specified period, daily cost, monthly cost projected to 30 days, and annual cost projected to 365 days.

A 65 W laptop used 6 hours a day draws 0.065 kW x 6 h = 0.39 kWh per day. Over a 30-day billing cycle that is 0.39 x 30 = 11.7 kWh. At $0.14 per kWh, roughly the midpoint of the typical US residential rate, the monthly cost is 11.7 x 0.14 = $1.64.

One of four values, Voltage (V), Current (A), Resistance (Ω), or Power (W), is solved from the other two, which are entered directly. The fundamental relationships applied are V = I x R, P = V x I, P = I² x R, and P = V² / R. The solved value appears alongside the formula derivation.

Settings controls the number of decimal places shown in results and a step-by-step formula view, which shows the symbolic formula followed by substituted values for each derivation.

Electricity consumption data informs budgeting decisions, equipment selection, and energy efficiency planning across residential, commercial, and educational settings.

• Home Energy Auditing: comparing the running cost of appliances such as refrigerators, washing machines, and HVAC systems, by wattage and daily usage, identifies which devices consume the most electricity over a billing period and builds a household consumption profile.
• Renewable Energy Planning: daily and annual kilowatt-hour consumption for a home or workshop sizes a solar panel array or battery storage system; a 200 W workshop light running 10 hours daily consumes 60 kWh per month, a figure that feeds directly into how many panels to install.
• Electronics Prototyping: Ohm's Law mode finds the correct resistor value for an LED circuit; a 5 V supply and a target current of 20 mA return 250 ohms of resistance and 0.1 W of power dissipation.
• Classroom Instruction: the relationships between voltage, current, resistance, and power in a physics or electrical engineering course show through the step-by-step formula display, which walks through each derivation with substituted values.
• Landlord Utility Estimation: electricity cost for common-area lighting, hallway HVAC units, or shared laundry machines, projected against the local rate and billing cycle, supports splitting utility charges among tenants.
• Server Room Budgeting: annual electricity cost for rack-mounted servers rated at 500 W each, run 24 hours per day at commercial electricity rates, forecasts operational expenses.
• Appliance Comparison Shopping: competing appliance models, compared by wattage, project monthly and annual operating cost at a local utility rate before a purchase decision.