Efficiency Calculator

Compare useful output energy against input energy to get efficiency and the losses.

About Efficiency Calculator

Efficiency is a simple ratio, but its value lies in the losses it implies. Converting those losses into annual energy and cost is what turns a percentage into a business case for replacement. A few points of efficiency on a continuously running machine is worth more over its life than the difference in purchase price.

Formula

Efficiency

Efficiency = useful output ÷ total input × 100

losses: Input less useful output, almost always dissipated as heat

Worked example

With the default values below, Efficiency Calculator returns Efficiency of 78.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Energy or power inminimum 0.01 W: 1,000 W
Useful energy or power outminimum 0 W: 780 W
Hours of operation per dayaccepts 0–24 h: 8 h
Energy price per kWhminimum 0: 0.15

Results

Efficiency: 78.00%
Losses: 220.00 W
Annual Energy Lost: 642.4 kWh
Annual Cost of the Losses: $96.36
Rating: B — Good

Step by step

1Values used
2Efficiency
3Efficiency= 78.00
4Losses= 220.00 W
5Annual Energy Lost= 642.4 kWh
6Annual Cost of the Losses= 96.36
7Rating= B — Good

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Efficiency calculated?

Efficiency = useful output ÷ total input × 100 Efficiency is a simple ratio, but its value lies in the losses it implies. Converting those losses into annual energy and cost is what turns a percentage into a business case for replacement.

Why does Efficiency matter?

A few points of efficiency on a continuously running machine is worth more over its life than the difference in purchase price.

What values do I need to enter?

This calculator takes 4 inputs: Energy or power in, Useful energy or power out, Hours of operation per day, Energy price per kWh. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.