How To Use a Roof Shingles Calculator For Roofing Estimates

Using a roof shingles calculator to estimate how many bundles of roof shingles you will need for your home seems logical, intuitive and easy. But still among the most frequently asked questions on this site is about how to use a roof shingles calculator! There are dozens and dozens of free online roof shingles calculator programs on the Web that anyone can use to estimate roof materials. But each is slightly different, and requires that you input specific data related to your roof. So let’s talk about using a roof shingles calculator and the points you’ll need to know in order to get the highest value from using one.

Broadly speaking, there are two ways to estimate the quantity of shingles you will need for your roof replacement. Both depend upon correctly measuring the area of your roof, and factor in the requirement for extra shingles to cover loss from breakage, wastage and overlaps.

You can order roof shingles by the bundle, or by roof squares (i.e. 100 square feet). Usually roof shingles are bundled in a way that 3 bundles are needed to cover 100 square feet. Each bundle will have around 30 shingles. In the case of heavier shingles, there will be fewer shingles per bundle in order to make it easy to transport the bundles, and so you may require 4 to 5 bundles per square.

Measurement Method of Using a Roof Shingles Calculator

In the measurement method, which is the most accurate, you will actually measure the roofing area and then calculate how many shingle bundles will be necessary to cover it. If your roof has simple planes, then the area can be computed pretty easily by just measuring the length and breadth, multiplying the two to give you the square footage.

However, many roofs have more complex geometrical arrangements, making it a little harder to get accurate measurements done. Also some roofs are hard to walk up, and so measurements may need to be done on the ground, with extrapolations being carried out to factor in for elevation. A roof shingles calculator can then be used to estimate how many shingles will be necessary to roof this area.

Sheet Count Method of Using a Roof Shingles Calculator

Another method that some contractors prefer when the roof sheathing is exposed is called the sheet-count approach. This does not require that you climb upon the roof, and can run an estimate from the ground itself. When the roof is sheathed with 4×8 feet panels, you know that each panel is 32 square feet – and by counting the number of panels that make up your roof area and multiplying it by 32, you get a fair estimate of the roof area. In the case of partial sheets, you can make allowance for the reduced area and subtract it from the whole.

From this estimation it is simple to use a roof shingles calculator to decide how many bundles of shingles you will need to buy. Each bundle will cover 33 square feet, which is just about the same as one panel’s area of 32 sq.ft. Ordering one bundle per sheet of roof sheathing is a good rule of thumb.

Shingle Count Method of Estimating Roof Shingles

If your existing roof hasn’t yet been torn down then you can use a simpler method to estimate shingle requirement – counting the older shingles. Going row by row, you could count the number of tabs, and then multiply the count by 5″ (which is the usual width of the exposed tab) and divide by 12 to get the length of the roof area in feet.

Then plug the number into your roof shingles calculator to arrive at an estimate of the number of bundles of shingles you’ll have to order.

Additional Shingles For Wastage

One area where your roof shingles calculator will not be able to help is in deciding how many additional shingles you need to order. This number will vary depending upon your skills and expertise with installing roofing shingles, as there will inevitably be more broken shingles and incorrectly cut ones when you’re just getting started.

In addition, there are certain areas of wastage that can’t be avoided, such as projections like chimneys and vents, or coming up against walls and angles where the shingle must be cut or trimmed. That’s why ordering extra shingles is important, because otherwise you’ll be forced to wait for a re-order towards the end – which may be prolonged if the manufacturer happens to run out of stock of the particular roofing shingles you’ve been using.

Where’s a Roof Shingles Calculator Indispensable?

Some roofs are complex. They have multiple hips and valleys. They have varying planes, even irregular shapes. They may have many projections like dormers, chimneys and eaves. To simplify the area calculations in such roofs, you can break down the entire building into rectangles and right angled triangles, and then measure as many edges as possible to get the sides of rectangles and triangles.

You then use something complex formulas to enter the data into roof shingles calculators which will spit out the computed area measurements of the complex roof. The finer details of this computation is beyond the scope of this report, but it probably isn’t something you’ll need to worry about either. After all that’s what a roof shingles calculator is for.

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