In short. A power cut costs more than the hours the lights are off. The true figure adds the restart time after each outage, the staff paid to stand idle, and the product scrapped or spoiled every time the supply drops. Put your own figures into the calculator below to get the cost per outage, per month and per year. That number tells you how much reliable standby power is worth to your business.
Who this page is for: factory owners, plant and maintenance managers, finance teams preparing a case for standby power, hospital and hotel administrators, cold-chain and food businesses, and anyone deciding whether to buy, upgrade, rent or properly maintain a generator.
Key facts
- The real cost of an outage = lost hours × (contribution lost per hour + idle staff cost per hour) + scrap or spoilage for each outage.
- Lost hours are longer than outage hours, because every outage is followed by restart and recovery time.
- Many short outages often cost more than one long one, because each brings its own restart time and scrap.
- Use contribution (sales value minus the variable costs you no longer spend), not sales value, or the answer is overstated.
- Penalties, damaged equipment and lost customers are real costs too. Add them by hand where you can estimate them.
Calculate your outage cost
Enter your own figures. The calculator starts with sample values that are only a starting point; replace each one with your plant’s numbers.
Lost hours = outage hours + (restart time × number of outages). Monthly cost = lost hours × (contribution lost per hour + idle staff cost per hour) + (scrap per outage × number of outages). Yearly cost = monthly cost × 12. These are your own business losses, not equipment prices.
The method, step by step
The calculator uses four simple steps. You can check its arithmetic by hand.
- Lost hours per month = outage hours per month + (restart or recovery hours per outage × outages per month).
- Monthly cost = lost hours × (contribution lost per hour + idle staff cost per hour) + (scrap or spoilage per outage × outages per month).
- Cost per outage = monthly cost ÷ outages per month.
- Yearly cost = monthly cost × 12.
Getting each input right
Outage hours per month
Take the total time the supply was off during working hours, from your own records, the controller’s event log on the existing set, or a power-quality logger. Use a typical month rather than the worst. If outages vary by season, work out a summer month and a monsoon month separately.
Outages per month
Count each interruption separately, including the short ones. A two-second dip that stops a line is an outage for this purpose, because it triggers a full restart.
Contribution lost per hour
This is the money the business does not make while production is stopped. For most plants it is sales value per hour minus the variable costs no longer spent, such as raw material and the electricity that would have been used. Do not use sales value: the material you did not consume is not lost.
If lost output can be made up later through overtime, the true cost is the overtime premium and any extra wear, not the full contribution. If the line already runs at full capacity, lost output is gone for good and the full contribution counts.
Idle staff cost per hour
Wages and salaries paid while people cannot work: operators, supervisors, packing and dispatch staff. Use the cost to the business, including allowances, not only basic pay.
Restart or recovery hours per outage
The time from supply returning to the line producing good output again. Plastics, glass, food processing, printing, textiles and chemical plants often need far longer to recover than the outage itself: barrels and dies reheat, ovens and boilers return to temperature, machines are re-homed and computers reboot. Time it on the next outage.
Scrap or spoilage per outage
Material lost at each interruption: a part-moulded shot, a ruined batch, a fabric run that must be cut out, spoiled dairy or cold-chain stock, a burnt print run, a failed test sample. Value it at its cost, not its selling price.
Penalties and other losses (add by hand)
Some costs do not fit a per-hour figure but can matter more than everything else:
- Late-delivery penalties and contract service-level charges.
- Equipment damage from abrupt shutdowns: motors, drives, compressors and electronics.
- Data loss, corrupted files and IT recovery.
- Lost customers and reputation, especially in hospitality and healthcare.
- Safety and regulatory exposure, for example in hospitals, laboratories and cold chains.
Estimate a yearly figure for these and add it to the calculator’s yearly cost.
Why restart time and outage count matter so much
Suppose a plant has 6 hours of outage a month. In one month it comes as one 6-hour cut; in another, as twelve 30-minute cuts. If restart takes 45 minutes each time, the first month loses 6.75 hours, but the second loses 6 + (0.75 × 12) = 15 hours, more than twice as much, plus twelve lots of scrap. That is why businesses on supplies with frequent short interruptions often gain the most from automatic standby power, and why a generator with an AMF panel that takes over within seconds is worth more than one that waits for someone to start it. Where even a short break forces a full restart, the controls and drives that trip also need a UPS to ride through the transfer.
What the result tells you
| If your yearly outage cost is… | It usually means… | Typical next step |
|---|---|---|
| Small compared with your running costs | Outages are a nuisance, not a business risk. | Maintain the existing set well; consider an AMC so it starts when needed. |
| Significant, mostly from restart time and scrap | Transfer speed matters more than size. | Add or upgrade an AMF panel; protect sensitive loads with a UPS. |
| Significant, and outages are long | Duration matters; the whole load needs covering. | Size a set for the full critical load. See generator sizing. |
| Very large, or penalties dominate | A single set is itself a risk. | Consider redundancy (N+1) and a resilience review. See critical power. |
| High for a few months a year only | The problem is seasonal or project-based. | Compare ownership with rental power using rent vs buy. |
Worked example (illustrative): a food-processing unit
A food-processing unit near Hyderabad runs two shifts. In a typical month its records show 8 outages totalling 10 hours. After each outage the cooking and packing line takes about 45 minutes to return to steady output. Each interruption spoils a part batch.
| Input | Value |
|---|---|
| Outage hours per month | 10 h |
| Outages per month | 8 |
| Contribution lost per hour | ₹18,000 |
| Idle staff cost per hour | ₹3,500 |
| Restart or recovery time per outage | 0.75 h |
| Scrap or spoilage per outage | ₹6,000 |
- Lost hours per month = 10 + (0.75 × 8) = 10 + 6 = 16 hours.
- Monthly cost = 16 × (18,000 + 3,500) + (6,000 × 8) = 16 × 21,500 + 48,000 = 3,44,000 + 48,000 = ₹3,92,000.
- Cost per outage = 3,92,000 ÷ 8 = ₹49,000.
- Yearly cost = 3,92,000 × 12 = ₹47,04,000, before any penalties or equipment damage.
Note that the 6 hours of restart time add 60 % to the 10 hours of actual outage. For this unit, an AMF set that takes over in typically 10–30 seconds cuts each outage to a short break. The restart time and spoilage fall as well only if the line rides through that break, for example with the cooker controls, drives and PLC on a UPS; otherwise the line still restarts every time.
The figures are illustrative. Use your own records.
Outage record sheet
Keep this for a month before you use the calculator. Real records beat estimates.
| Date | Supply off (time) | Supply back (time) | Outage duration | Line back to steady output (time) | Recovery time | Scrap or spoilage (description and cost) | Remarks |
|---|---|---|---|---|---|---|---|
| Month totals |
Exceptions and cautions
- Overstating contribution. Using selling price instead of contribution can make the answer several times too high, and weakens the case with a finance team.
- Recoverable output. If the plant has spare capacity and lost output is made up later, use the overtime premium instead of contribution.
- Partial stoppages. If only some lines stop, use the contribution of those lines only.
- Existing standby. If a set already covers some loads, count only the losses that still occur, including those during a manual changeover.
- Not a quotation. This calculator values your losses. It does not price equipment or services.
Common mistakes
- Counting only the hours the supply was off, and ignoring restart time.
- Ignoring short dips that stop machines but are never written down.
- Using sales value instead of contribution.
- Leaving out spoilage because it is “only a few kilograms” each time.
- Working from the worst month, then losing credibility when the average is lower.
- Forgetting penalties and equipment damage, which can dwarf everything else.
What to send us
Send your outage record sheet or the calculator’s result, a list of the loads that must keep running, and a short description of how long each process takes to recover. Use the application engineering enquiry, or WhatsApp the details to 98852 01608. A service engineer will suggest whether you need faster transfer, more capacity, redundancy or simply better maintenance, and you can use Get price for the recommended arrangement.
Questions engineers ask
Why is restart time included?
Because production does not resume the moment supply returns. Machines reheat, re-home and reboot. That recovery time is lost production just like the outage itself, and it is repeated at every interruption.
Should I use revenue or contribution per hour?
Contribution: the sales value of lost output minus the variable costs you no longer spend, such as raw material. Using revenue overstates the loss.
What are the calculator’s default values?
Six outage hours a month, four outages, ₹25,000 contribution and ₹4,000 idle staff cost per hour, half an hour of restart time and ₹10,000 scrap per outage. They are only a starting point; replace them with your own figures.
Where do penalties go?
Estimate them as a yearly figure and add them to the calculator’s yearly cost by hand. The same applies to equipment damage, data loss and lost customers.
Are many short outages worse than one long one?
Often, yes. Each outage brings its own restart time and scrap, so twelve short cuts can cost more than one long cut of the same total length.
What do I do with the answer?
Compare it with what reliable standby power would cost you to own and run, or to rent. The result shows whether the priority is faster transfer, more capacity, redundancy or better maintenance.
Related pages
- Rent vs buy
- Lifecycle cost
- Generator sizing
- Generator kVA and kW sizing calculator
- AMF panels
- Critical power
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer. Last updated 5 November 2026.