2 squares per box
RecommendedSiding Is Sold by the Square
A square is 100 square feet of finished wall. Every siding product, from vinyl to fiber cement to cedar, is quoted and ordered in squares, so the whole estimate comes down to converting wall area into that unit and then adding a waste allowance.
Siding squaresSquares = (total wall area minus openings) divided by 100, then multiplied by 1.10 for waste
Use 1.10 on a plain rectangular elevation and 1.15 on a cut up elevation with dormers, bays, multiple gables or a lot of windows. Round up to the next whole unit the product is sold in.
Measuring rectangular walls
Take each wall as a rectangle: width x height, measured from the bottom of the starter strip to the top of the wall. Add the walls together. A 30 ft by 40 ft two story house with 9 ft walls has a perimeter of 140 feet and a wall height of 18 feet, which is 2,520 square feet of rectangular wall before gables.
Measuring gables
A gable is a triangle, and the area of a triangle is half the base times the height. Measure the base at the level where the rectangular wall stops, measure straight up to the peak, multiply, and halve it.
Gable areaSquare feet = (base width in feet x peak height in feet) divided by 2
A 30 ft wide gable rising 8 ft to the ridge is 30 x 8 divided by 2, which is 120 square feet. A house with two identical gable ends adds 240 square feet.
A gambrel or a clipped gable is two triangles or a triangle plus a trapezoid. Break any odd shape into rectangles and triangles, work each out, and add them. Dormer cheeks are small triangles that are easy to miss and they add up on a house with three or four of them.
Subtracting openings
Measure each window and door and subtract its actual area. A common approach is to deduct only openings larger than about 10 square feet and let the small ones absorb into the waste allowance, since the offcut from around a small window rarely gets reused. A garage door at 16 ft by 7 ft is 112 square feet and always comes out of the total. Leaving a full house of openings in the estimate can overstate an order by 10 percent or more.
Waste and How Much to Add
Ten percent is the working figure. It covers cutting to length, the offcut at the end of each course, mistakes and the pieces damaged in handling. Push it to 15 percent when any of the following apply:
- Multiple gables, dormers or a roof line with several changes of direction.
- A large number of windows relative to the wall area.
- Board and batten or any vertical product, where cuts cannot be staggered along a course.
- A pattern or a wood grain product where matching matters and short pieces cannot be used.
- A diagonal or angled wall, which produces a bevel offcut on every course.
On a very plain single story rectangle with few windows, 7 to 8 percent is often enough, but the saving is small and running short mid job risks a different production lot with a slightly different color.
Vinyl Comes in Boxes of Two Squares
Most vinyl siding ships in a box holding 2 squares, which is 200 square feet of coverage. Divide the required squares by 2 and round up to get the box count. A house needing 27.5 squares takes 14 boxes, which is 28 squares, and the small surplus is useful for future repairs. Keep two or three panels in the garage, because vinyl colors are discontinued regularly and a matched replacement in five years is often impossible.
Siding typeTypical unit soldInstalled cost per square, 2026 range
Vinyl lapBox of 2 squares400 to 800 dollars
Insulated vinylBox of 2 squares700 to 1,200 dollars
Fiber cement lap12 ft planks, sold per piece900 to 1,600 dollars
Engineered wood lap16 ft planks, sold per piece800 to 1,400 dollars
Cedar bevelBundles by linear foot900 to 1,800 dollars
Steel or aluminumPanels, sold per piece900 to 1,600 dollars
Board and batten, engineered4 ft x 8 ft or 4 ft x 9 ft panels700 to 1,300 dollars
Those are wide national ranges for material and labor together, and they move with region, house height, access, tear off of the old siding and the amount of trim detail. Get three local quotes before setting a budget.
Soffit and Fascia
Soffit is the underside of the roof overhang and fascia is the vertical board at the edge of the rafter tails. Neither is included in wall area and both have to be measured on their own.
Soffit area is the eave run in linear feet multiplied by the overhang depth in feet. A house with 160 linear feet of eave and a 16 in overhang has 160 x 1.333, which is 213 square feet, or 2.13 squares. Vented soffit is used where the attic draws intake air and solid soffit is used elsewhere, and most houses need a mix.
Fascia is bought in linear feet to match the eave and rake runs. Rake runs, the sloped edges at a gable, are longer than the horizontal distance they cover, so measure them along the slope rather than off a plan. Add 10 percent to both soffit and fascia for waste and mitred corners.
Trim Is Measured in Linear Feet
Trim accessories are not part of the square count. Each one is a separate line item measured in linear feet, and forgetting them is the single most common gap in a siding estimate.
- Starter strip. One run around the base of every wall being sided. Equal to the perimeter of the house at the bottom course.
- J channel. Runs around every window and door, along the top of walls under the soffit, and along the rake edges of gables. Per opening it is the perimeter of that opening plus about a foot for corners, so a 3 ft by 5 ft window needs about 17 linear feet.
- Outside corner posts. One per outside corner, cut to the full wall height. Sold in 10 ft or 12 ft lengths, and a two story corner needs a splice.
- Inside corner posts. Same idea at every inside corner, common on an L shaped or U shaped footprint.
- Utility trim and undersill. Used at the top course under the soffit and above windows, wherever a panel has to be cut lengthwise and locked in.
Add 10 percent to every trim run for cuts and mitres, and buy corner posts in a single length that covers the wall height where possible, since a spliced post is visible from the street.
House Wrap and Nails
House wrap is a weather resistive barrier and most local codes require one behind siding. A standard roll is 3 ft by 100 ft, covering 300 square feet, and wide rolls at 9 ft by 100 ft cover 900 square feet and go up much faster on a two story wall. Divide the gross wall area, before opening deductions, by the roll coverage and round up, because wrap is lapped 6 inches horizontally and 12 inches at vertical seams and that overlap eats material. Seams need wrap tape, roughly one roll of tape per two rolls of 9 ft wrap.
Fasteners depend on the product. Vinyl siding typically takes about 1 to 1.5 pounds of roofing nails per square, driven so the panel still slides. Fiber cement takes about 2 to 3 pounds per square of hot dipped galvanized or stainless nails, blind nailed at every stud. Always specify corrosion resistant fasteners, and use stainless within a few miles of salt water, since electro galvanized nails will streak rust down a wall within a season.
Details That Change the Estimate
Vinyl and metal siding expand and contract with temperature. Vinyl panels have to hang loose on their nails with about 1/32 in of gap under the nail head, and they need 1/4 in of clearance at every trim end, doubled to 3/8 in when installing below about 40 degrees Fahrenheit. Nailed tight, a vinyl wall buckles in the first hot afternoon.
Flashing is separate from trim and not optional. Head flashing goes over every window and door, kickout flashing goes where a roof edge meets a wall, and step flashing runs up any roof to wall intersection. Water gets behind siding by design, and flashing is what sends it back out.
Codes and prices are localWeather resistive barrier requirements, flashing details, fastener schedules, fire separation distances and wind exposure ratings are all set by local code and vary widely. Prices vary by region and by season. Confirm the requirements with the building department and get three local quotes before committing to a budget.