Free Siding Calculator

How to Calculate Siding for Your Home

Our siding calculator helps you estimate materials for vinyl, fiber cement, wood, and other siding types. Enter your wall dimensions, gable areas, and window/door openings to get accurate estimates.

How to Use This Siding Calculator

1. Total wall length: measure along the base of every wall you are re-siding and add the lengths together. A 30 ft by 50 ft house sided on all four walls is 160 ft.
2. Wall height: measure from the bottom edge of the siding up to the soffit. If parts of the house have different wall heights, run the calculator once for each part and add the results.
3. Gable height and width: measure the base of the triangle under the roof peak and its height from that base to the peak. The calculator takes one gable, so for two matching gables enter twice the width. Clear both fields if there is no gable.
4. Window and door area: multiply the width by the height of each window and door and add them up. This area is subtracted from the walls. If you leave it blank, the counts below stand in for it at 12 sq ft a window and 20 sq ft a door.
5. Number of windows and doors: count the openings in the walls you are re-siding. J-channel is worked out around each one, so ten small windows get more trim than one big opening of the same area. Leave both blank and the area is treated as 12 sq ft windows.
6. Calculate: the squares figure is the net area plus 10% waste, divided by 100. Round it up to whole squares when you order, and buy the starter strip and J-channel listed with it.

The fields start with the worked example below, so replace them with your own measurements, in feet or in meters with the unit switch. The siding type does not change the area, the squares or the 10% waste: every material is estimated by the square, and the waste figures published for each material differ from one source to the next, so the calculator applies the same 10% to all of them. What the type changes is how you buy it, which the results spell out: vinyl and aluminum come in cartons rated in squares, while fiber cement and wood are sold by the plank or board, so you convert with the coverage per piece on the product sheet. The cost shown is one national installed range of $4 to $13 per sq ft of net wall area. For prices by material, see the siding cost guide.

What is a Square of Siding?

A "square" is an industry-standard measurement equal to 100 square feet of siding coverage. This is how contractors estimate and price siding, and how vinyl and aluminum siding cartons are rated.

How Much Extra Siding Should I Order?

We recommend ordering 10-15% extra siding to account for:

• Cuts and waste around windows and doors
• Mistakes during installation
• Damaged pieces that may need replacement
• Complex architectural features

The Siding Formula

This calculator uses the same math contractors use for a first-pass material estimate:

1. Wall area: wall height x total wall length (measure each wall and add the lengths together)
2. Gable area: 0.5 x gable width x gable height for each triangular gable section
3. Net area: gross wall area minus the total area of windows and doors
4. Order quantity: net area plus 10% waste, expressed in squares (1 square = 100 sq ft)

Trim pieces are estimated separately: starter strip runs the full length of all walls plus 10%. J-channel goes around each opening, all four sides of a window and both sides and the top of a door: the window and door area is split evenly across the openings you count, each is measured as a square, and 20% is added for cuts and overlaps. With no counts the area is treated as 12 sq ft (about 3 ft x 4 ft) windows; with no area each window counts as 12 sq ft and each door as 20 sq ft (3 ft x 6 ft 8 in).

Worked Example: Single-Story Ranch

A single-story home with 120 ft of combined wall length, 9 ft walls, one gable 30 ft wide and 5 ft tall, and 150 sq ft of windows and doors:

• Wall area: 9 ft x 120 ft = 1,080 sq ft
• Gable area: 0.5 x 30 ft x 5 ft = 75 sq ft
• Gross area: 1,080 + 75 = 1,155 sq ft; net after openings: 1,155 - 150 = 1,005 sq ft
• With 10% waste: 1,005 x 1.1 = about 1,106 sq ft, or 11.1 squares
• Trim: about 132 ft of starter strip and 208 ft of J-channel. With no window and door counts, the 150 sq ft is taken as 12.5 windows of 12 sq ft, each about 13.9 ft around; enter 10 windows and 2 doors instead and the J-channel comes to about 195 ft

At the 2026 installed range of $4-$13 per sq ft of net wall area, that project lands roughly between $4,000 and $13,100 depending on material, region, and site conditions.

Siding Cost Factors and Common Mistakes

Material choice is the biggest cost driver. Vinyl is usually the least expensive to install, fiber cement costs more in labor because it is heavy and needs special cutting tools, and wood or engineered wood products sit at the top of the range. Cost also varies by region, the condition of the existing walls, and whether old siding needs to be removed and hauled away.

• Waste factor: 10% covers simple rectangular walls; go to 15% with gables, dormers, and lots of openings
• Old siding: tear-off adds cost but lets you inspect the sheathing and install a new water-resistive barrier
• Common mistakes: measuring one wall and multiplying, forgetting gables, and skipping trim pieces (starter strip, J-channel, inside/outside corners) in the order
• Insulation: adding a layer of rigid foam or insulated siding raises material cost but can improve comfort and energy bills

See siding on your own house before you buy

A quantity is only half the decision. Color and profile are the part people second-guess, and siding is an expensive thing to change your mind about once it is on the wall. The free HomeGPT AI exterior design tool works from a photo: upload a picture of the front of your house and it renders that same house with different siding materials, board profiles, and colors, so you can compare a warm cedar tone against dark board-and-batten on your own facade instead of on a two-inch showroom sample.

It runs in the browser with no app to install and no signup, so you can take the photo on your phone and have options side by side in a couple of minutes. See how it works on the AI exterior design page, or go straight to the exterior design tool and upload your photo. Once a direction looks right, come back here to price the material.