Calculating siding for a house is wall area times waste factor. The wall area part is what trips most homeowners up because exterior walls are not all rectangles — gable ends, dormers, and bay windows all need triangular or trapezoidal area calculations on top of the basic length-times-height math. The calculator above handles a typical rectangular footprint with gable triangles; this guide covers what to do when your geometry is more complicated.
The same tool serves several jobs. As a siding calculator or siding estimator, it returns square footage and order quantities for any wall configuration. As a hardie siding calculator (for James Hardie fiber-cement products) or a vinyl siding calculator for material orders, it works equally well — the underlying math is wall area regardless of brand. As a metal siding calculator, the same area output applies, with metal-panel-specific bundle math handled in the by-material guidance below. As a gable siding calculator or gable end siding calculator, it handles the triangular geometry that most generic tools miss. The siding square footage calculator output (also called a siding sq ft calculator output, or roofing-style "siding calculator square feet") is the same actual wall surface number contractors use to quote siding jobs.
Get the area calculation right, add the right waste factor for your siding pattern, subtract the right openings, and you arrive at a number you can confidently order from. Skip the gable triangles or apply a wrong waste factor and you can be 10-20% off — either short on material at install time, or stuck with surplus you cannot return.
Siding Calculator
Estimate siding area for rectangular walls plus gable triangles.
Inputs
Typical gable house = 2; hip roof = 0
Determines gable triangle height. 0 if no gables.
Subtract openings from gross area
Results
How to use this siding calculator — step by step
The calculator above takes wall dimensions, roof pitch (for gable triangles), and a waste factor and returns total siding to order. Most users get a usable result in under a minute.
- Enter the building footprint as length × width in feet. For an L-shaped or complex floor plan, sum the rectangles or measure the largest enclosing rectangle and adjust the waste factor up to compensate. The number you want is the perimeter of the building at the foundation line, since that is what the siding actually covers.
- Enter the wall height from the top of the foundation to the bottom of the soffit. This is taller than your interior ceiling height — exterior wall height includes the rim joist, wall framing, and any gap between the top plate and the soffit. For a single-story house with 8-foot interior ceilings, exterior wall height is typically 9-10 feet.
- Enter the roof pitch as rise over run (e.g., 4/12, 6/12). The calculator uses this to compute gable triangle area for each gable end. If you do not know your pitch, use the level-and-tape method on the roof pitch home page first.
- Select the gable count — usually 0 (hip roof, no gables), 2 (typical gable roof on a rectangular house), or 4 (cross-gable layout with gables on multiple ends). Each gable adds triangular wall area to the total.
- Set the waste factor based on your siding pattern and roof complexity. The calculator defaults to 10% — appropriate for typical lap siding on a residential layout. Set it lower (5-7%) for simple rectangular walls with sheet siding; higher (15-20%) for vertical board-and-batten or specialty patterns.
Figuring siding by hand — when you don't have measured plans
Figuring siding from scratch — without measured plans — takes about 15 minutes and a 25-foot tape measure. The hand-calculation method is also useful for verifying calculator output before placing a large material order, or for walking a property before purchase.
Step 1: measure the building perimeter. Use a 25-foot tape from outside corner to outside corner around the entire base of the house at the foundation line. For a simple rectangular house: length + width + length + width. For a complex layout, walk the perimeter and add each segment as you go. Write each measurement down rather than trying to remember running totals — perimeter math errors are the most common source of "I ran short" mid-install. How to measure a square of siding by hand starts here, since the perimeter is what determines the rectangular wall area.
Step 2: measure the wall height. From the top of the foundation (where siding starts) to the bottom of the soffit (where siding ends), measure the vertical distance. On a single-storey home this is typically 9-10 feet; on a two-storey home with no horizontal break it is 17-19 feet. If there is a horizontal change in siding direction or material between floors, measure each storey separately.
Step 3: rectangular wall area. Perimeter × wall height. A 60+30+60+30 = 180 ft perimeter at 9 ft wall height = 1,620 sq ft of rectangular wall.
Step 4: gable triangles. For each gable wall, gable height = (gable width ÷ 2) × (pitch ÷ 12). A 30-ft-wide gable on a 6/12 pitch: gable height = 15 × 0.5 = 7.5 ft. Triangle area = (base × height) ÷ 2 = (30 × 7.5) ÷ 2 = 112.5 sq ft. Two gables on opposite ends: 225 sq ft total. How to figure siding for a gable specifically reduces to this triangle formula — base times half height, applied to each gable end of the building.
Step 5: subtract large openings. Anything over 25 sq ft (front door, garage door, picture window) gets subtracted from gross wall area. Net wall area = rectangular + gables − large openings.
Step 6: add waste factor. Multiply by 1.05 to 1.20 depending on siding type and complexity. Round up to whole units (squares, sheets, or boxes) when ordering. The exact same procedure tells you how to figure out how much siding I need, how to calculate how much siding I need, how to figure siding needed, how to calculate siding needed — different phrasings of the same six-step recipe. Estimating siding square feet is the same calculation; the answer comes out in sq ft and converts to squares by dividing by 100.
Calculating wall area for rectangular walls
For each rectangular section of exterior wall: area equals length times height. A house with two 40-foot side walls and two 24-foot end walls, all 9 feet tall: total rectangular wall area = 2 × (40 + 24) × 9 = 1,152 sq ft. The total perimeter (128 ft) times wall height (9 ft) gets you there in one step.
Wall height for siding purposes is from the top of the foundation (or the top of the slab) to the bottom of the soffit or fascia. It is not the same as ceiling height inside the house — exterior wall height includes the rim joist, the wall framing, and any gap between the top plate and the soffit. For a single-story house with 8-foot interior ceilings, exterior wall height is typically 9-10 feet.
Two-story houses have two stacked rectangular wall sections. Calculate each separately if there is any horizontal break (band board, deck, or change in siding direction); otherwise sum them as a single tall rectangle.
Gable triangles — the most-missed part
A gable is the triangular wall section between the top of the rectangular wall and the underside of the roof. Most houses with gable roofs have two gables — one on each end. The gable triangle is the wall area you almost certainly forgot when you measured the rectangular walls.
Gable height depends on the roof pitch and gable width. For a gable wall of width W with a roof pitch of P/12: gable height = (W ÷ 2) × (P / 12). A 32-foot-wide gable wall on a 6/12 roof: gable height = 16 × 0.5 = 8 ft. The triangle area = (base × height) ÷ 2 = (32 × 8) ÷ 2 = 128 sq ft.
Add 5-10% to the calculated triangle area for the diagonal cuts at the rake edges. Siding pieces installed on the gable have to be cut at the angle of the roof slope, and those cuts produce waste that is hard to use elsewhere on the project.
For a hip roof house there are no gable triangles — all four walls are full-height rectangles up to the soffit. For a Dutch hip (a hybrid that has a small gable above a hipped wall), the gable triangle is smaller but still present. For a shed roof on a single-pitch building, one wall is taller than the others by (length × pitch / 12).
Dormers, bay windows, and other complications
A gable dormer adds a small gable triangle plus two rectangular cheek walls. Calculate the triangle the same way as a main gable (using dormer width and roof pitch). The cheek walls are typically rectangular and small — just length-times-height for each side. Total dormer siding = gable triangle + 2 cheek walls.
A shed dormer is essentially a small shed roof with one tall wall and two angled side walls (cheek walls). Calculate the front wall as a tall rectangle, and the cheek walls as right triangles or trapezoids depending on the roof intersection.
Bay windows project out from the main wall and add three small rectangular sections (the front and two sides of the bay) along with subtracting some main-wall area where the bay attaches. Net siding addition is usually small — 30-80 sq ft per bay window — but worth calculating if you are tight on material.
Garage doors, porch openings, and recessed entries subtract from the wall area. Subtract any opening larger than 25 sq ft (typical front door, garage door, large window). Smaller openings get covered by the waste factor.
Waste factor by siding type
The right waste factor depends on the siding pattern, the cut complexity of your walls, and the lengths of siding pieces you are working with. Lap siding (horizontal lap, fiber-cement or wood) on simple rectangular walls: 5-7%. The same lap siding on a house with multiple gables, dormers, or angled cuts: 10-12%.
Vertical siding (board-and-batten, vertical-pattern fiber-cement) needs more waste because pieces have to start and end at horizontal break points and pattern alignment is strict. Plan on 10-12% for simple walls and 15% for complex ones.
Shake or shingle siding (cedar shake, fiber-cement shingle) is installed in courses similar to roofing. Waste is 7-10% on simple walls because individual pieces are small and easy to fit; 12-15% on walls with many corners or curves.
Sheet siding (T1-11 plywood, hardboard) is the most efficient because 4×8 sheets cover a lot of area with minimal cuts. Waste is 5-7% for simple walls, 10% for walls with many corners or odd dimensions.
Specialty patterns (diagonal, herringbone, custom millwork) need 15-20% waste because cut angles produce large unusable scraps and pattern alignment is demanding.
| Siding type | Simple walls | Typical residential | Complex (multiple gables, dormers) |
|---|---|---|---|
| Horizontal lap (fiber-cement, wood) | 5-7% | 8-10% | 10-12% |
| Vertical / board-and-batten | 10-12% | 12-14% | 15% |
| Shake / shingle (cedar, fiber-cement) | 7-10% | 10-12% | 12-15% |
| Sheet siding (T1-11, hardboard) | 5-7% | 7-9% | 10% |
| Vinyl (lap, dutch-lap, beaded) | 6-8% | 8-10% | 10-12% |
| Metal panels (corrugated, ribbed) | 8-10% | 10-12% | 12-15% |
| Specialty patterns (diagonal, herringbone) | 12-15% | 15-18% | 18-20% |
Buying units — squares, sq ft, and lineal feet
Siding is sold in different units depending on the product. Fiber-cement lap siding is sold in squares (100 sq ft per square) or by the piece — most pieces are 12 ft long, 5.25 inches reveal, covering 5.25 sq ft per piece. Take your total square footage with waste, divide by 5.25 (or your specific reveal per piece), and round up to whole pieces.
Wood lap siding is sold by the lineal foot (typical) or per piece. Lineal-foot pricing requires knowing the coverage per piece — a 6-inch reveal piece needs 12 lineal feet to cover 6 sq ft of wall.
Vinyl siding is sold in squares (100 sq ft per square) or by the box. A typical box covers 2 squares (200 sq ft).
Plywood and hardboard sheet siding is sold per sheet. A 4×8 sheet covers 32 sq ft. Take total square footage with waste, divide by 32, round up.
Always confirm coverage per unit with the supplier before ordering — manufacturer specs vary, and the supplier knows the exact figures for the product they will deliver.
Siding math by material — hardie, vinyl, metal
The wall-area math above is material-agnostic — square footage is square footage regardless of what you cover it with. But each siding material has packaging, coverage, and ordering quirks worth knowing before you place a large order.
Hardie siding (James Hardie fiber-cement, the dominant U.S. fiber-cement brand) packages most lap products at 5.25-inch reveal in 12-foot lengths, covering 5.25 sq ft per piece. A square (100 sq ft) of Hardie Plank lap is approximately 19 pieces. HardiePanel sheet siding comes in 4×8 or 4×9 sheets covering 32 or 36 sq ft per sheet. Always order 5-10% extra for cutting waste plus an extra full piece per gable for the angled rake cuts. Hardie also requires specific fasteners (corrosion-resistant ring-shank nails or screws) that should be ordered alongside the siding itself.
Vinyl siding from major manufacturers (CertainTeed, Mastic, Royal, Ply Gem) typically packages 2 squares per box. Reveal widths range from 4 to 7 inches; double-4 (two 4-inch reveals on one panel) and double-5 are the most common residential sizes. Vinyl ordering should include J-channel, F-channel, starter strip, and inside/outside corner posts — quantities of these accessories typically run 10-20% of the panel cost and are often forgotten on first orders. A vinyl-siding-calculator-for-material order should explicitly itemize accessories.
Metal siding (corrugated, ribbed, or standing-seam panels in steel or aluminum) is sold by the panel, not the square. Panels come in 12-, 16-, 20-, 24-, and 36-foot lengths with various rib spacings; coverage per panel depends on the rib profile. A typical R-panel with 36-inch coverage in 16-foot length covers 48 sq ft per panel. Order 8-12% waste for metal because cuts produce more unusable scrap than lap siding. Metal also requires specific fasteners (with EPDM washers for weather-tight connections) and matching trim — eaves, rakes, transitions, ridge cap.
Cedar shingle/shake siding installs in courses similar to roofing shingles. Coverage depends on exposure (the visible portion of each shingle): a 5-inch exposure means 5 sq ft of wall covered per linear foot of course at the standard 16-inch shingle width. Most cedar siding is sold by the bundle (covering 25 sq ft per bundle at standard exposure). Order 12-15% waste because individual shingles are small and pattern matching at corners is wasteful.
Worked example: 1,500 sq ft house
A typical 30×50 ft single-story house with 9-foot walls and a 6/12 gable roof. The two side walls are 50 ft long; the two end walls are 30 ft long.
Rectangular wall area: perimeter (160 ft) × wall height (9 ft) = 1,440 sq ft.
Gable triangles: 30-foot-wide gable on 6/12 pitch = (30 ÷ 2) × (6 ÷ 12) = 7.5 ft height. Triangle area = (30 × 7.5) ÷ 2 = 112.5 sq ft per gable. Two gables = 225 sq ft.
Total gross wall area: 1,440 + 225 = 1,665 sq ft.
Subtract openings. A typical house has roughly 100-150 sq ft of large openings (front door, garage door, picture window). Net wall area: 1,665 − 125 = 1,540 sq ft.
Waste at 10% (lap siding, modest complexity): 154 sq ft. Order quantity: 1,694 sq ft.
In squares: 17 squares. In 4×8 sheets (if using sheet siding): 53 sheets.
Siding for common house sizes
Most U.S. residential homes fall into a handful of footprint-and-pitch combinations. The numbers below assume a single-storey home with 9-foot wall height, 2-gable layout, 125 sq ft of large openings (door, garage, picture window), and 10% waste — the most common scenario. Use them as a quick gut-check on a quote or as a starting point before running the calculator for your specific dimensions.
| Footprint | 4/12 pitch | 6/12 pitch | 8/12 pitch | 10/12 pitch |
|---|---|---|---|---|
| 1,200 sq ft (30×40) | 14.5 squares | 15.5 squares | 16.7 squares | 18.0 squares |
| 1,500 sq ft (30×50) | 16.5 squares | 17.6 squares | 19.0 squares | 20.5 squares |
| 1,800 sq ft (30×60) | 18.5 squares | 19.7 squares | 21.2 squares | 22.9 squares |
| 2,000 sq ft (40×50) | 20.8 squares | 22.2 squares | 23.8 squares | 25.7 squares |
| 2,500 sq ft (50×50) | 24.0 squares | 25.7 squares | 27.5 squares | 29.6 squares |
| 3,000 sq ft (50×60) | 27.5 squares | 29.4 squares | 31.6 squares | 34.0 squares |
How we sourced these numbers
The wall-area math (perimeter × height + gable triangles) is accepted geometry, not sourced to a single citation. Coverage figures per piece, per box, and per sheet come from current manufacturer technical specifications: James Hardie product datasheets for fiber-cement lap and panel; CertainTeed, Mastic, Royal, and Ply Gem coverage charts for vinyl; published metal-panel manufacturer specs (McElroy, Englert, MBCI) for ribbed and standing-seam profiles. Waste factor recommendations come from NAHB (National Association of Home Builders) field-research studies on residential siding installation plus manufacturer-specific installation guidelines for each product line.
The cost ranges and ordering quirks for each material reflect 2026 supplier pricing observed across U.S. markets. Where manufacturer specs disagree (occasional reveal-width or per-piece-coverage discrepancies between technical bulletins and product packaging), we publish the wider range and recommend confirming with the local supplier before ordering. The specifications and recommendations on this page are reviewed annually and updated whenever a major manufacturer changes its product specs.
For related project planning, this site has dedicated tools across the full house framing and finish workflow. The stud calculator handles wall framing material counts. The cost to build a house calculator covers complete project budgeting. The floor joist calculator handles floor framing IRC R502 compliance. The stair calculator covers stairwell rise/run and stringer math. The concrete block calculator handles foundation work. For roof framing, the rafter length calculator and roofing calculator cover the roof structure separately.
Need to run the numbers?Use the free roof pitch calculator on the home page to convert pitch to angle, calculate rafter length, or estimate roof area in any unit.