This program was created for the United Kingdom residents who wish to learn how much their appliances are costing them to run. Electricity Cost Calculator for British Gas comes with a user-friendly interface, lets you change the default kWh prices and appliances' usage ratings, and is free of charge.
You can also use this utility to calculate your electricity bills. Just select the average consumption for each appliance within your house and enter the current kWh price. You can also choose the approximate hours of use per month for the electrical device. The program will then display the cost to run the selected appliance for 1 month.
Electricity Cost Calculator for British Gas provides you with a long list of electrical appliances: iron, toaster, laptop, microwave, TV, refrigerator, light bulb, and many others. I think it would be easier to choose the proper device if all appliances would be found within a list on a separate window, rather than clicking the Next and Previous buttons.
In addition, you have direct access to the home URLs of other applications that could help you calculate different types of fees (for instance, postage fees).
In conclusion, I'd say it's worth installing this free app on your Mac if you're a UK resident and wish to calculate your electricity bills.