The cost of a new roof can vary widely depending on the shape, size and other features it includes. Dormer windows, chimneys, skylights or even just a steep pitch can all affect the price considerably, and removing the old shingles comes with a cost as well. Rather than paying someone to give you an estimate or doing complex calculations with a pencil and paper, you can use simple online tools to quickly figure the rough cost of replacing the roof of your house.
Measure the length and width of your home, to determine the basic dimensions of your roof. Measure the length of the ridge vent. On gable roofs this will be the same as the overall length, but on hip roofs it will be shorter. If you don't know the slope of your roof, climb a ladder positioned at the end of the house and measure the rise of the roof, from the vent to the height of the eaves. Write down all measurements for later use.
Observe your roof and write down all its features. This includes the number of chimneys and skylights, as well as its overall complexity. Is it a simple gable roof? A hip roof? Or one with several different ridges and valleys?
Go to the Roofing Calculator website (see Resources) and use the online roof pitch calculator. Enter the width, length and rise of your roof and click "Calculate roof pitch." The results will be given to you as the number of inches rise per horizontal foot. Write it down.
Return to the home page and use the main calculator to determine the likely cost of a new roof. Enter all the relevant data---the basic dimensions, roof pitch, general level of complexity, layers of shingles to be removed, number of stories above ground, number of skylights, chimneys and the length of the ridge vent.
Click "Calculate Roof Cost" and wait a few seconds for your results. The site will display a list of prices by roofing material, with the annual energy savings of energy-efficient roofs. The actual cost of a new roof may vary somewhat, but most reputable, licensed contractors will charge something close to the estimate given.