What is energy cost per part?

It is the electricity cost of running a machine divided by the good parts it produced in the same window. The formula is Machine kW times Run Hours times $/kWh, divided by Good Units Produced. In the worked example, 22 kW over 8 hours at $0.12/kWh costs $21.12, and across 1,400 parts that is $0.015 per part. It isolates energy from the rest of unit cost.

How do I measure the actual Machine kW instead of using nameplate?

Clamp a power meter or three-phase logger on the machine's supply and record average kW during normal steady-state production, ideally over a full cycle including idle and active phases. Most machines draw well below nameplate, so a 30 kW-rated unit might average 22 kW. Log for at least one full shift to capture the real duty cycle, then use that average, not the plate rating.

What is a good energy cost per part benchmark?

There is no universal target because it depends on process intensity. Light machining or assembly often lands under $0.01 per part, while molding, heat treat, or die casting can run $0.05 to $0.20. Judge it as a share of total unit cost: if energy is under 2 percent, do not chase it; if it exceeds 5 to 10 percent, an efficiency project likely pays back.

Why did my energy cost per part go up even though the machine did not change?

The denominator usually drives it. Falling yield or more scrap means the same kWh spreads over fewer Good Units, raising cost per part. Check whether Good Units Produced dropped. Other causes are a higher blended $/kWh from new demand charges, longer Run Hours per part due to slower cycles, or a worn component increasing actual power draw. Isolate which variable moved.

Should I use kW or kWh in the calculation?

Both. Machine kW is instantaneous power, and multiplying by Run Hours converts it to energy in kWh, which is what you are billed for. In the example, 22 kW times 8 hours equals 176 kWh. Then multiply kWh by the $/kWh rate to get dollars. If you already have a kWh reading from a submeter, skip the kW-times-hours step and go straight to kWh times rate.

How is energy cost per part different from total cost per part?

Energy cost per part is only the electricity slice, $0.015 in the example. Total cost per part also includes material, direct labor, tooling amortization, maintenance, and overhead. Energy is typically a small fraction, so use this formula when comparing process alternatives on energy specifically or quantifying an efficiency project's savings, not as a standalone measure of whether a part is profitable.

Energy and Sustainability

Energy Cost per Part Formula

Energy cost per part allocates the electricity cost of running a machine to each unit produced. Use it when building a complete unit cost model, comparing process alternatives on energy, or quantifying savings from an efficiency project.

Formula

Energy Cost per Part = (Machine kW x Run Hours x $/kWh) / Good Units Produced

Variables

Machine kW: Average power draw of the equipment during production in kilowatts
Run Hours: Operating hours in the measurement window
$/kWh: Blended electricity rate including demand charges, in dollars per kilowatt-hour
Good Units Produced: Number of good parts produced in the same period

Understanding the Energy Cost per Part Formula

Energy cost per part isolates the electricity component of unit cost by tying a machine's power draw to the parts it actually made. It answers a narrow but real question: how many cents of electricity are embedded in each good part. On the shop floor this matters because energy is often lumped into overhead and spread evenly, hiding which processes are power-hungry. In the example, 176 kWh at $0.12 produces $21.12 of cost across 1,400 parts, or $0.015 each.

Pull Machine kW from a clamp meter or power logger reading actual average demand during steady-state running, not the nameplate. Run Hours is the machine's operating window, not shift length, so subtract downtime. The $/kWh should be a blended rate that folds in demand charges, since a single kW figure understates your true billed rate by 20 to 40 percent. Count only Good Units Produced; scrap consumed energy but carries no value, so including it flatters the number.

Compare the result against the part's total cost. At $0.015 per part on a component selling for a few dollars, energy is trivial and not worth chasing. On a high-throughput, energy-intensive process like injection molding or induction heating, energy cost per part can hit $0.05 to $0.20 and becomes a real lever. Rising numbers month over month usually signal a worn tool, a leaking system, or falling yield diluting the denominator.

Worked Example

A machine draws 22 kW and runs 8 hours producing 1,400 parts. Electricity rate is $0.12/kWh.

Energy used = 22 x 8 = 176 kWh
Energy cost = 176 x $0.12 = $21.12
Cost per part = $21.12 / 1,400 = $0.015

Result: $0.015 per part energy cost

Common Mistake

Using nameplate kW instead of actual average power draw. Most machines run below nameplate during steady-state production. Using nameplate overstates energy cost. Measure actual demand with a power meter for the most accurate result.

Frequently Asked Questions

What is energy cost per part?: It is the electricity cost of running a machine divided by the good parts it produced in the same window. The formula is Machine kW times Run Hours times $/kWh, divided by Good Units Produced. In the worked example, 22 kW over 8 hours at $0.12/kWh costs $21.12, and across 1,400 parts that is $0.015 per part. It isolates energy from the rest of unit cost.
How do I measure the actual Machine kW instead of using nameplate?: Clamp a power meter or three-phase logger on the machine's supply and record average kW during normal steady-state production, ideally over a full cycle including idle and active phases. Most machines draw well below nameplate, so a 30 kW-rated unit might average 22 kW. Log for at least one full shift to capture the real duty cycle, then use that average, not the plate rating.
What is a good energy cost per part benchmark?: There is no universal target because it depends on process intensity. Light machining or assembly often lands under $0.01 per part, while molding, heat treat, or die casting can run $0.05 to $0.20. Judge it as a share of total unit cost: if energy is under 2 percent, do not chase it; if it exceeds 5 to 10 percent, an efficiency project likely pays back.
Why did my energy cost per part go up even though the machine did not change?: The denominator usually drives it. Falling yield or more scrap means the same kWh spreads over fewer Good Units, raising cost per part. Check whether Good Units Produced dropped. Other causes are a higher blended $/kWh from new demand charges, longer Run Hours per part due to slower cycles, or a worn component increasing actual power draw. Isolate which variable moved.
Should I use kW or kWh in the calculation?: Both. Machine kW is instantaneous power, and multiplying by Run Hours converts it to energy in kWh, which is what you are billed for. In the example, 22 kW times 8 hours equals 176 kWh. Then multiply kWh by the $/kWh rate to get dollars. If you already have a kWh reading from a submeter, skip the kW-times-hours step and go straight to kWh times rate.
How is energy cost per part different from total cost per part?: Energy cost per part is only the electricity slice, $0.015 in the example. Total cost per part also includes material, direct labor, tooling amortization, maintenance, and overhead. Energy is typically a small fraction, so use this formula when comparing process alternatives on energy specifically or quantifying an efficiency project's savings, not as a standalone measure of whether a part is profitable.