A machine that is switched on but not making anything still draws power. Hydraulic pumps, coolant, chillers, heaters, control cabinets and unloaded compressors all keep running. With 30 machines idling 3 hours a day at 2.5 kW each, that is 67,500 kWh a year, and at ₹8.5 a unit about ₹5.7 lakh a year paid for nothing. This calculator puts your own numbers on it.
How the calculator works
The calculator takes five inputs:
- Machines. How many machines you are counting. Group similar machines together, for example all hydraulic presses or all VMCs, and run each group separately.
- Idle hours a day with power on. The average hours each machine is energised but not producing: waiting for material, for an operator, for first-piece approval, through lunch, or left on at the end of the shift.
- Idle power draw per machine (kW). What one machine draws while idle, not its nameplate rating. Measure it with a clamp meter while the machine sits idle. Nameplate kW overstates idle draw on some machines and understates it on others.
- Tariff (₹/kWh). Your all-in energy charge per unit from the bill: energy charge, plus fuel and power purchase adjustment, plus electricity duty, divided by units.
- Working days a year.
The formulas:
kWh per year = machines × idle hours a day × idle kW × working days
Cost per year = kWh per year × tariff
The calculator counts energy charges only. Demand charges on your contract demand (kVA) are left out, because idling usually doesn't change the peak you are billed on. Idling can still matter on a Time-of-Day tariff, where the same kWh costs more in peak slabs.
Worked example (India)
A machining or moulding shop. All inputs are assumptions for illustration, and they are the calculator's defaults. Replace the idle kW with a clamp-meter reading as soon as you have one.
| Input | Value |
|---|---|
| Machines | 30 (assumption) |
| Idle hours a day with power on | 3 (assumption) |
| Idle power draw per machine | 2.5 kW (assumption) |
| Tariff | ₹8.5/kWh (assumption) |
| Working days a year | 300 (assumption) |
| Output | Working | Result |
|---|---|---|
| Idle machine-hours a day | 30 × 3 | 90 h |
| Idle kWh a day | 90 × 2.5 | 225 kWh |
| Idle kWh a year | 225 × 300 | 67,500 kWh |
| Cost per day | 225 × 8.5 | about ₹1,913 |
| Cost per year | 67,500 × 8.5 | ₹5.74 lakh |
What 2.5 kW idle means. For a small CNC with a coolant pump and a hydraulic unit, 2.5 kW idle is a plausible figure. For an old hydraulic injection moulding machine it can be far too low. An energy guide for moulders says the base load of standard hydraulic machines (the energy used while idling, such as during cooling) can amount to 75% or more of their total energy consumption, against typical base loads of 10–20% for all-electric and hybrid machines (An Energy Saving Guide for Plastic Injection Molding Machines, AMI with Tangram Technology). As a rough reading, a hydraulic machine averaging 20 kW with a 75% base load draws about 15 kW whenever it sits idle with the motor on, six times the default. That is why one measurement per machine group matters more than any other input.
About the tariff. ₹8.5 is an assumption, not a published rate. Industrial tariffs are set by each state commission, and several have held rates flat recently. For example, Gujarat retained FY 2027 tariffs at the previous year's level. Your all-in rate per unit comes from your own bill.
What typical numbers look like
- Unloaded compressors still draw a lot. The US Department of Energy's compressed air tip sheet uses a worked example in which an unloaded compressor draws 25% of full-load power (DOE Compressed Air Tip Sheet #1). Seattle City Light's guidance states that "unloaded compressors consume 30% of the power of a fully loaded compressor". Treat these as orders of magnitude. The real share depends on the controls, the age of the unit and the receiver size.
- Hydraulic machines are the heavy idlers. As noted above, base load can be 75% or more of total energy use on standard hydraulic moulding machines, and typically 10–20% on all-electric and hybrid machines (AMI/Tangram guide).
- CNC idle draw in India. We found no credible published survey of idle power draw for CNC machines in Indian shops. Research measurements vary widely with machine size and auxiliaries such as coolant, chillers and chip conveyors, so measure your own.
What this number does not tell you
- Whether the idle time could be avoided. Some idling is necessary. Hydraulic oil and moulds need to stay at temperature, and spindles need warm-up. Switching off for a 10-minute wait can cost more in scrap and restart time than it saves in power. The calculator prices the energy. It does not say which idle hours you can cut.
- The cost of the idle hours themselves. Energy is usually the small part. An idle machine-hour also carries depreciation, the operator and overhead. The machine hour rate calculator puts a number on that, and it is typically many times the power cost.
- Demand charges and Time-of-Day effects. Energy charges only. If idling falls inside a peak slab, the true cost per unit is higher than a flat rate suggests.
- What cameras can see. Cameras cannot read kW. They can show when a machine is lit, warm and unattended with no parts moving. That tells you when and where to put the clamp meter. It is not a meter reading. See Idle Machines, Lights and Compressors: The Energy Bill Cameras Can Explain.
- Plant loads outside the machines. Lighting, ventilation, compressors serving the whole plant and chillers idle too. Run them as separate lines in the calculator with their own kW.
Related guides
- Idle Machines, Lights and Compressors: The Energy Bill Cameras Can Explain
- Spindle Utilisation: What 25%, 45% and 70% Mean on an Indian Floor
- What One Hour of Downtime Actually Costs an Indian Factory (₹)
- Waiting for First-Piece Approval: The Inspector Queue That Idles Your CNCs (₹)
- Machine utilisation monitoring options compared
FAQ
How do I calculate the energy cost of an idle machine? Multiply the machine's idle power draw in kW by the idle hours, then by your tariff per unit. Thirty machines idling 3 hours a day at 2.5 kW is 225 kWh a day, or 67,500 kWh over 300 days. At ₹8.5 a unit that is about ₹5.74 lakh a year.
How much power does a CNC machine draw when idle? It depends on the machine and its auxiliaries: coolant pump, hydraulic unit, chiller, chip conveyor and control cabinet. There is no reliable single figure. Clamp-meter the incoming supply while the machine sits idle, with everything left on the way your operators normally leave it.
Should we switch machines off during short stops? Not always. Machines that need warm-up, or hydraulics and moulds that must stay at temperature, can lose more in scrap and restart time than they save in power. Switching off is usually worth it for long, predictable gaps such as lunch, shift-end waits and no-order periods.
Does an unloaded compressor still use electricity? Yes. The US Department of Energy's example assumes 25% of full-load power for an unloaded compressor, and a US utility's guidance says 30%. Turning off compressors you don't need, or controlling them better, is one of the most common energy savings.
Why is my idle energy cost small compared with my idle machine cost? Because power is only one part of what an idle hour costs. Depreciation, operators, overhead and lost output usually cost far more than the electricity, so treat the energy figure as the smaller of the two losses.
Mama reads a factory's existing cameras and each morning tells the owner where machine and line hours were lost the day before. Mama can draw a camera plan for the machines that most often stand idle with power on. Leave an email or phone in the form below.