Roofing Calculator

Roofing Calculators Save Time and Money

Nobody roofs a house for fun. It’s hard, sweaty, dirty work.

Whether you’re a DIY’er or a roofing contractor, you don’t want to be up on the roof for one minute longer than you must. And you don’t want to buy more roofing material than you have to.

This is where a roofing calculator can make a big difference. Taking the time to measure a few things and run the numbers can save you hours of labor and hundreds of dollars and cut down on trips to supply stores. These days, that means significant savings on gas, too.

Having a reliable roof size calculator can make short work of determining how many square feet of shingles you’ll need to pick up at the building supply store. You can think of your roof size calculator more as a roofing material calculator. Knowing the area is the first step in understanding how much to buy.

What to Look for in a Roofing Calculator

Make sure the tool you’re using to calculate does more than simply determine your roof’s square footage. While that will matter, it is only the first step in getting the roof replaced. What matters most is how much material we will need to buy. A good roofing area calculator will output:

• Quantity of shingle bundles
• Quantity of rolls of roll roofing
• Quantity of rolls of #15 felt
• Quantity of rolls of #30 felt

Why Do You Need All Those Numbers?

Shingle Bundles

Asphalt shingles will be your most significant expense and heaviest item. You don’t want to buy any more than you need. Returning a few bundles to the store is no big deal. Returning dozens is a backbreaking and time-consuming chore. Worse, having to drop everything and grab a few more to finish the job is frustrating as it brings everything to a screeching halt. A good roofing materials calculator will give you this number with a bit of a buffer to keep things running smoothly.

Roll Roofing

This is a cheaper, more practical option for sheds or very low-pitched roofs. A good calculator will allow you to compare the quantity of rolling roofing with regular shingles. Once you have both numbers, making a quick cost comparison is easy to see if it’s worth it.

#15 Felt

Because 15# felt is thinner than 30#, you’ll end up with fewer rolls for the same square footage. If your vehicle is small, you want to condense trips; this could be a deciding factor.

#30 Felt

Because it is thicker and heavier, each roll has to be smaller (72 feet vs. 144 feet). You end up with twice as many rolls to cover the same area. It’s good to know about that when planning your project and trips.

Gathering the Numbers for Input

To get our roofing material numbers, you should take a few measurements to let the calculator do its magic.

1. House Base Area

This simple measurement is taken on the ground with a long tape measure. If you’re lucky enough to have a simple square or rectangle-shaped home, measure one short and one long side. Multiply the two to get a square footage (sq. ft.) number.

For instance, if your home is 70 feet long in the front and 20 feet wide at the side, the calculation is 70 × 20 = 1,400. Therefore, your house base area is 1,400 sq. ft.

If you have an odd-shaped home, as most of us do, there’s a slightly different method. Go inside the house, measure every room’s square footage, and add and summarize. You’ll get a number that will do just fine while not being 100% accurate and slightly smaller than the actual area.

2. Roof Pitch

The pitch of a roof is expressed as the rise over run. Or, put another way, how many inches does it rise vertically for every 12 inches it extends horizontally? A roof that rises 4 inches for every 12 inches of the horizontal run has a 4-in-12 pitch.

One way to get the pitch is to go into the attic with a long level, a pencil, your tape measure, and a friend who owes you a favor.

• Make a mark 12 inches from the end of the level.
• Locate the end of the roof rafter where it meets the joists and have your friend hold it perfectly level.
• Measure from the 12-inch mark straight up vertically until you reach the rafter. That number is the number of inches the roof rose by 12 inches.

If that number is 6, our roof pitch is 6/12. If the number is 8, our pitch is 8/12, and so on. For calculations below, let’s use a pitch of 4/12 as that is relatively standard.

3. The Eaves

Most homes have an overhang to protect the exterior walls from the elements. The area under that overhang is what is referred to as the eaves. Measure the distance from the exterior wall out to the edge of the roof. You will probably need a ladder for it.

We’ll assume the eaves extend 2 feet. This is our “Eaves Stick Out” number.

Price (optional)

If you’ve done your homework and know how much your shingles and felt cost per square foot, the roofing area calculator can become a roofing price calculator in a snap.

You can typically find the price per square foot on the shelf front tags at most home building supply centers. Add the cost per sq. ft. of the shingles and felt to come up with one number. $4 per sq. ft. is a reasonable number for our example.

Results:

• 1,841 square feet of roof area
• 56 bundles of shingles, or
• 19 rolls of roll roofing
• 5 rolls of #15 felt, or
• 10 rolls of #30 felt
• Cost $7,365

Most suppliers will happily take returns of unopened shingle bundles and roll roofing, so it’s a good idea to use the 10% buffer that is factored into the calculator.

What We Gained

Here’s what we learned by taking a minute to use the calculator instead of making a rough guess based on the size of our home.

1. You know your roof size.
2. You know how many trips to the building supply store you will need. If you can safely haul 30 bundles, you have two trips. No need to weigh down the minivan with one huge load.
3. Most importantly, you know how much this project will cost. You can budget for supplies. Or, if you’re a roofer, and they quote you $10,000 for supplies, you’ll know something isn’t right and can renegotiate as needed.

Recommended Uses

Even if you have an extremely simple roofline, computing the home area, adding the eave length, and factoring in pitch is a complicated equation. Getting any part of it wrong means wasted money and time.

The roofing area calculator becomes indispensable if you have a complicated roofline with multiple valleys, dormers, hips, and rake edges. You can arrive at reasonably accurate numbers by breaking the roof into simpler shapes and taking measurements. Doing so by hand increases the likelihood of errors.

Hiring a contractor can be nerve-wracking. Are they overbilling? Are they being truthful about the amount of materials they are charging? With a roofing material calculator, you can check them for real numbers. It eliminates the possibility of being defrauded if they ask you to pay for more shingles than you need.

Whether you’re a DIY’er, a roofing contractor, or hiring a contractor, a detailed roofing calculator is a must-have to get your project started on a smooth path.