Field calculator
Energy cost calculator (kWh and dollars)
Putting a dollar figure on a running load is the starting point for any efficiency, retrofit, or operating-cost decision. The energy used per day equals the load in kilowatts times the hours it runs, and the cost equals those kilowatt-hours times the rate in dollars per kWh, multiplied by 365 for the year. Enter the load, the run hours, and your rate. To get the kW from a nameplate in watts, divide by 1000, and for a motor or variable load use the real running draw rather than the nameplate maximum. This calculator covers the energy (consumption) charge, which is exactly what an LED lighting retrofit, a high-efficiency motor or VFD, or a scheduling change reduces, so it is handy for sizing the payback on an upgrade. Remember a commercial bill also carries demand charges billed on the monthly peak demand in kW, plus fixed customer fees and taxes, so for a real number use the utility's actual rate schedule and tariff, not just the energy rate.
Result
Energy cost: kWh per day = load in kW × hours run per day, and the cost = kWh × the rate in dollars per kWh (times 365 for the year). Enter the load, the run hours, and the rate. To get the kW from a nameplate in watts, divide by 1000; for a motor, use the actual running load, not the nameplate maximum. This estimates the energy (consumption) charge, which is what efficiency upgrades like LED retrofits and high-efficiency motors reduce. A commercial bill also carries demand charges billed on the peak kW plus fixed fees and taxes, so use the actual utility rate schedule and tariff for a bankable number.
Worked example
A 5 kW load runs 8 hours a day at $0.14/kWh. What does it cost to run?
- Power5 kW
- Run time8 hrs/day
- Rate$0.14/kWh
- Daily energy = 5 × 8 = 40 kWh. Daily cost = 40 × $0.14 = $5.60/day.
- Annual cost = $5.60 × 365 = $2,044/year.
$5.60 a day, about $2,044 a year. Cutting run time or right-sizing the equipment is where the savings live.
anvilfield.com/calculators/energy-cost-kwh-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Energy cost FAQ
What is electrical submetering?
Electrical submetering measures electricity below the utility's revenue meter, so you know what a single tenant, load, or system used instead of only the whole building. It uses a meter and current transformers on each circuit, and the data is the owner's, for billing tenants, allocating cost, or finding energy waste.
What is the difference between a submeter and the utility meter?
The utility's revenue meter measures the entire service and is what the power company bills against. A submeter measures a portion downstream, a tenant or a load, and belongs to the building owner. The utility meter sets the bill from the grid. Submeters divide that bill or track a load inside the property.
What is a current transformer?
A current transformer, a CT, is a sensor that clamps around a conductor and outputs a small signal proportional to the current flowing, letting a meter read high amperage without the full current passing through it. Split-core CTs open to retrofit live conductors. Solid-core CTs are closed rings used when the circuit is open.
What is revenue-grade metering?
Revenue-grade metering is accurate enough to bill against, defined in the US by ANSI C12.20 with accuracy classes 0.1, 0.2, and 0.5, where the number is the percent error at full load. Monitoring-grade meters run Class 0.5 to 1, fine for energy management but usually not enough for tenant billing under state rules.
Why should I never open a CT secondary under load?
A current-output CT with its secondary open becomes a constant-current source driving an open circuit, saturating its core and generating a high voltage at the terminals that can exceed 1000 V. That can shock or kill you and destroys the CT. Short the secondary with the shorting block before any disconnect while current flows.