Each appliance in your home uses electricity at a certain wattage, which you can use to calculate how many kilowatthours the electricity company charges you for it every month. Your clothes dryer is a good demonstration of this calculation since, according to the Minnesotabased Otter Tail Power Company (OTPC), it uses more wattage than most other appliances yet costs relatively little on your utility bill.
Wattage

OTPC estimates that your dryer uses 5,000 watts of electricity. Since this may not represent your dryer's actual wattage, you should calculate it yourself to find out how much electricity it really uses. Look on the machine to find its amperage and voltage. Multiplying the number of volts and amps of electricity your dryer uses tells you exactly how many watts it uses.
Calculating KilowattHours

Divide your dryer's wattage by 1,000 to determine how many kilowatthours of electricity it uses. Using the OTPC statistic of 5,000 watts, you find that the average dryer uses about 5 kWh. Multiply this figure by the number of hours you use the dryer every month to find out how many kilowatthours the electricity company charges you for using this appliance alone. You can estimate by multiplying the number of loads of laundry you dry each month by the number of minutes required to dry a load, then dividing the result by 60. This is roughly the number of hours for which you use the dryer each month. OTPC estimates a median usage of 17 hours per month, resulting in 85 kWh total per month.
Cost

Read your latest utility bill to find out how much your electricity company charges you per kilowatthour. If you can't find it on the bill, contact the company for help. The U.S. Energy Information Administration reports that the average price per kilowatthour is 11.2 cents as of 2011, so you can use this to estimate your own cost. Multiply the price per kilowatthour by the kilowatthours of energy your dryer uses each month to calculate how much your dryer costs on your utility bill. The cost of a dryer that uses 85 kWh per month is about $9.50 on average.
Environmental Impact

Cost isn't the only result of using your dryer. The electricity your dryer uses causes the emission of carbon dioxide into the atmosphere, which contributes to pollution. According to the University of Northern Iowa, one kilowatthour of electricity is equivalent to 2.34 lbs. of CO2 entering the atmosphere. With a dryer that uses 85 kWh per month, that's almost 200 lbs. of CO2. Using your dryer less often means more money in your wallet and less pollution to the environment.