Multi-Device Electricity Cost Calculator

About this calculator

A bill is the sum of a handful of things, and usually one or two of them dominate. People are often wrong about which: the device that feels expensive is frequently not the one costing the money, because cost is wattage multiplied by hours and a low-wattage device left on all day can beat a high-wattage one used briefly.

List what you run, and this ranks them by what each costs a month. The ranking is the useful part — it says where a change would actually make a difference.

How to use this calculator

1. Enter your rate per unit from your bill.
2. For each device, give it a name, its wattage from the rating plate, how many you have, and the hours a day it genuinely runs.
3. Leave unused rows at zero watts — they are ignored.
4. Read the list. It is sorted by cost, heaviest first.

The formula

Each device:  Watts x Quantity x Hours / 1000 = units a day
Total:        sum of all devices
Cost:         total units a month x your rate

The total power figure shown separately is what you would draw if everything ran at once. It is not the same as the consumption, which allows for the hours each device actually runs, and it is the figure that matters for sizing a supply rather than for a bill.

Worked example

Four devices at ₹8.50 a unit:

Fridge      150 W x  8 h = 1.20 units/day = Rs 306.00/month
Ceiling fan  75 W x 12 h = 0.90 units/day = Rs 229.50/month
Laptop       65 W x  8 h = 0.52 units/day = Rs 132.60/month
4 LED bulbs   9 W x  6 h = 0.22 units/day = Rs  55.08/month
                                    Total = Rs 723.18/month

The fan runs at half the fridge's wattage and costs three-quarters as much, because it is on for half as long again.

Notes and limits

• Eight rows on purpose. This is a way to find the expensive device, not an inventory system, and eight covers the question.
• No wattages are supplied for any device. They come from your own rating plates, because devices of the same description differ widely.
• Use running hours for anything thermostatic. A fridge is switched on all day but its compressor runs perhaps a third of it.
• The total is the energy cost of these devices. A bill also has fixed charges, slabs, fuel adjustment and duty, and anything not on your list.
• To size an inverter or a supply rather than a bill, use the power budget calculator.

What this calculation assumes

• Each device draws its entered wattage for its entered hours.
• The total power figure assumes everything runs at once; the consumption figure does not.
• The result covers the devices listed only, and is energy cost rather than a bill.