Reply from our Silentnight Expert:
Unfortunately you have not said what size of electric blanket you have purchased. For the double the approx wattage used would be as follows: -
Heat Setting No. 1 - 28 watts
Heat Setting No. 2 - 55 watts
Heat Setting No. 3 - 97 watts.
When on standby no electricity is consumed.
The actual cost will depend on the price your utility company charges you.