Calculating Power Usage

To help avoid any power cuts or dangerous conditions at your event, you can calculate how much power equipment will likely use, and use this when planning how to distribute power to equipment. You can also calculate how much power you will likely use for the duration of the event, and the cost associated.

Units

These are the units you will encounter when working with electrical supplies and equipment:

Unit	Abbreviation	Physics Term	Relevance
Volts	V	Potential Difference	The utility supply voltage, typically 230 or 120 Volts - check your country's on Wikipedia
Amps	A	Current	The maximum rating of power distribution equipment, often displayed on its casing
Watts	W	Power	The maximum energy consumption of an appliance

Calculations

If we know the values of two of the three above units, we can calculate the third:

Watts = Volts × Amps

Amps = Watts ÷ Volts

Volts = Watts ÷ Amps

Consumption

You can estimate the total power consumption you and your attendees equipment will require, and compare this estimate to what is available in a prospective venue, or use it to calculate your maximum number of attendees.

Typical Consumption

Equipment	Typical Consumption Watts
Gaming desktop	250
Gaming laptop	150
LCD monitor	50
CRT monitor	100
Games console	150
Microwave	1200
Toaster	1000
Electric oven	4000
Air conditioner	3000
Desk fan	25
Router	10
Network switch	25

PC Power Supply Ratings

It's very important to understand that the power rating of a PC power supply does not mean that it will draw that much power. A 1200 Watt power supply does not mean it is using anywhere near that value - it is the maximum power the PSU is able to supply.

An average gaming PC draws around 250 to 300 Watts while running a game, and more powerful gaming PCs can draw 300-400W.

Estimating Total Consumption

Once you have a list of all the equipment you need to power for your event, and all the appliances that will be used during the event, add up the consumption of all these items in Watts.

For example:

Item	Quantity	Each	Total
Gaming desktop	10	250 Watts	2500 Watts
LCD monitor	10	50 Watts	500 Watts
Gaming laptop	5	150 Watts	750 Watts
Router	1	10 Watts	10 Watts
Switch	1	25 Watts	25 Watts
Electric oven	1	4000 Watts	4000 Watts
		Total	7785 Watts

Now that we know the total consumption of all this equipment in Watts, we can use this value and the utility voltage to calculate the required supply current in Amps: If we know our supply voltage is 230 Volts, we can use the calculation Amps = Watts ÷ Volts from above:

Amps = 7785 Watts ÷ 230 Volts 7785 ÷ 230 = ~33.85 Amps

Knowing the equipment's total consumption in Amps will help us check the venue's supply is rated to provide this.

Supply

You can calculate the total number of Watts that can be safely and reliably supplied by a single breaker by using the calculation Watts = Volts × Amps from above.

For example, if we know our supply voltage is 230 Volts, and the breaker supplying our group of sockets is 16 Amps:

Watts = 230 Volts × 16 Amps

230 × 16 = 3680

So our answer is 3680 Watts can be safely supplied by this breaker.

Calculating Usage Costs

The venue may be interested in how much power you expect to use. Some of the monitoring options above will tell you after the event, but it is possible to approximately calculate usage, if you know the consumption of the equipment you will be using.

KiloWatt-Hours

The unit KiloWatt-Hour, abbreviated to kWh, is a measure of the amount of KiloWatts used for 1 hour. Electricity meters display the number of kWh used since the meter was installed, and this value is used by utility companies use to bill their customers.

A KiloWatt is 1000 Watts, so if two computers each consuming 500 Watts ran for 1 hour, that would equate to 1 KiloWatt-Hour of energy being consumed.

Calculations

Add up the consumption for all of your equipment in Watts, and multiply that by the number of hours you expect them to be running for, excluding any times where the equipment will be off.

For example:

50 computers × 400 Watts each × 24 hours = 480,000 Watts, or 480 kWh

To calculate the approximate cost, multiply this by the unit price from the utility company.

For example:

480 kWh × 18¢ = €86.40

Measuring & Monitoring

The above calculations give you approximate results, but it is also possible and useful to measure and monitor power useage to get a more accurate result. See Measuring & Monitoring Power Usage.