How to Estimate a Siding Job Step by Step

Siding bids rarely go wrong on the big numbers. They go wrong on the small stuff: a gable nobody measured, J-channel around twenty windows, a tear-off that turned out to be two layers deep. By the time the crew is done, the extra material and labor hours have eaten the profit. Here is a repeatable method for measuring, building a material list and pricing a siding job so the numbers hold up.

Measure wall area by elevation

Measure each elevation on its own: front, rear, left and right. Working elevation by elevation keeps you from missing sections and makes the scope easy to walk through with the homeowner.

1. Wall rectangles: length times height for each wall, from the starter line up to the soffit.
2. Gables: a triangle is base times height divided by 2. Measure from the top of the wall plate line to the peak.
3. Dormers, bump-outs and sided chimneys: measure them as separate pieces and add them in.
4. Openings: measure each window and door (width times height) and subtract. A common practice is to skip deducting small openings, since the material cut around them usually ends up as scrap anyway. Whatever rule you use, use it on every job.

Add it all up and divide by 100. In siding, one square equals 100 square feet, same as roofing.

Materials and waste

Net wall area is not your order. Add a waste factor based on how cut-up the house is. As a common practice, a simple box with few corners needs less, and a house with multiple gables, angles and lots of windows needs more. Many contractors work in the 10% to 15% range, but adjust it to your own track record and the manufacturer's guidance.

Beyond the siding itself, count these items:

• House wrap or water-resistive barrier: covers gross wall area, with the laps the manufacturer specifies. Include seam tape and flashing for windows and doors.
• Starter strip: linear feet along the perimeter where the siding begins.
• J-channel: around windows and doors (add up each opening's perimeter), under the soffit and along the gable rakes.
• Outside and inside corners: count them and measure their height. Corner posts come in fixed lengths, so round up by the piece.
• Trim: window surrounds, frieze board, utility trim under windows.
• Soffit: square feet (eave length times overhang depth). Decide on vented or solid based on attic ventilation.
• Fascia: linear feet along eaves and rakes.
• Fasteners: the type and length the manufacturer calls for.

Tear-off of old siding

Check what is underneath before you bid. Removing existing siding, repairing rotted sheathing and hauling debris is real labor and real cost. Price it per square and include the dumpster or dump runs. On homes built before 1978, painted surfaces may contain lead, and the work must follow the EPA RRP rule plus any state requirements.

Material options

• Vinyl: lowest cost and fastest install. It is hung loose so it can expand and contract.
• Fiber cement: heavier, more durable and more labor-intensive. It needs dust-controlled cutting tools and the clearances and finishing the manufacturer specifies.
• Engineered wood: a real wood look at a lighter weight than fiber cement. Cut edges need sealing, and the install has to follow the manufacturer's instructions to keep the warranty.

Labor

Labor is usually priced per square, but not every square costs the same. Adjust for:

• Wall height and whether you need staging, scaffolding or a lift.
• Number of corners, windows and cuts.
• Material type (fiber cement takes more time and more hands than vinyl).
• Trim, soffit and fascia, which are cleaner to price separately by the linear foot or square foot.
• Sheathing repairs, which work well as a per-sheet unit price.

Overhead and profit

Start with your direct cost: material, labor, tear-off and disposal, permits and equipment. Then add your overhead, the fixed cost of running the business spread across jobs (office, insurance, trucks, software, sales). That gives you total cost.

To get to a selling price, use margin, not markup:

Price = total cost / (1 - desired margin)

For a 30% margin, divide by 0.70. Watch out for the classic mistake of adding 30% to cost. That is markup, and it only leaves you about a 23% margin.

Example estimate

The numbers below are an example only. Material and labor pricing varies by region, product and season.

A 40 x 30 ft rectangular house with 9 ft walls and two gables on the 30 ft sides, 6 ft tall at the peak.

• Walls: 140 ft perimeter x 9 ft = 1,260 SF.
• Gables: 2 x (30 x 6 / 2) = 180 SF.
• Gross area: 1,440 SF.
• Openings: 12 windows at 3 x 5 (180 SF) and 2 doors at 3 x 7 (42 SF) = 222 SF.
• Net area: 1,218 SF.
• With 10% waste: 1,340 SF, so 14 squares rounded up.

Example costs:

• Siding: 14 squares x $150 = $2,100
• Trim, J-channel, corners, starter, soffit and fascia: $800
• House wrap, tape and flashing: $300
• Tear-off and disposal: $1,200
• Labor: 14 squares x $250 = $3,500
• Direct cost: $7,900
• Overhead (example 10%): $790
• Total cost: $8,690

Price at a 30% margin: $8,690 / 0.70 = $12,414. Gross profit is $3,724, which is 30% of the price.

Good, better, best options

Giving the homeowner three choices puts them in control and tends to raise the average ticket:

• Good: standard vinyl, house wrap and basic trim.
• Better: thicker or insulated vinyl, upgraded trim and new vented soffit.
• Best: fiber cement or engineered wood, full window trim and a complete soffit and fascia package.

Common mistakes

• Skipping gables or measuring them as full rectangles.
• Not counting J-channel and corner posts by the piece.
• Pricing tear-off without checking what is under the existing siding.
• Using the same waste factor on a simple ranch and a cut-up two-story.
• Confusing markup with margin and keeping less profit than you planned.

How RoofDesk helps

With RoofDesk you enter the measurements you take on site for each elevation and build the proposal from siding templates that already include good, better and best options, trade units (SQ, LF, SF) and waste factors. You track cost, overhead and profit per job, and the suggested price uses total cost / (1 - margin). The homeowner gets the proposal in English or Spanish, accepts and signs it from their phone, and you collect the deposit with an invoice they can pay by card online.

Frequently asked questions

How many square feet are in a square of siding?

One square of siding is 100 square feet. Divide total wall area, with waste included, by 100 to get the number of squares.

Should I subtract windows when measuring siding?

Yes, deduct large openings like doors, big windows and garage doors. Many contractors leave small windows in to cover cut waste. Pick a rule and apply it consistently.

What waste factor should I use for siding?

It depends on the complexity of the house. As a common practice, contractors use 10% to 15%, and more on homes with many gables and angles. Adjust based on your experience and the manufacturer's recommendations.

Book a demo

If you want to estimate siding faster and know your numbers on every job, book a RoofDesk demo and we will walk you through a siding proposal from start to finish.