Standing on the ground looking up at your house, you're wondering: do I have enough siding materials for this whole exterior, or am I going to come up short mid-project? A siding calculator removes the guesswork and tells you exactly what you need-before you hit the supply store.
What This Calculator Does
This siding calculator measures your home's exterior wall area and accounts for windows, doors, and other openings. It calculates the total square footage you need to cover, then converts that into the number of siding pieces, squares (100 sq ft bundles), or linear feet depending on your siding type. The result? No wasted money, no incomplete projects, and no return trips.
How to Use This Calculator
Start by measuring your home's perimeter-the total distance around the outside. Then measure the height from the foundation to the roofline. Multiply perimeter by height to get your gross wall area.
Next, subtract the openings: windows, doors, and any other gaps. Measure each window and door frame, calculate their areas, and subtract the total from your gross wall area. This gives you your net siding area.
If your siding is lap siding (like vinyl or wood planks), you'll lose coverage to overlaps. A 6-inch exposure on 8-inch boards means only 6 inches covers new wall per course. Add 15-20% to account for this. For shake or shingle siding, add 10-15% for waste and cutting. The calculator handles these adjustments automatically, but knowing why they matter helps you understand the final number.
Enter your measurements, select your siding type, and the calculator delivers the exact quantity you need in multiple formats: total square feet, number of squares, linear feet, or bundle count depending on how your supplier sells it.
The Formula Behind the Math
Gross wall area = House perimeter × Wall height
Net siding area = Gross wall area − (Window area + Door area + Other openings)
Coverage adjustment = Net area × (1 + waste factor)
Example:
Your house is 80 feet around (perimeter) and 20 feet tall (foundation to roof). Gross area = 80 × 20 = 1,600 sq ft.
You have four window openings at 3 ft × 4 ft each = 48 sq ft total. Two doors at 3 ft × 7 ft each = 42 sq ft. Total openings = 90 sq ft.
Net area = 1,600 − 90 = 1,510 sq ft.
Add 15% waste for lap siding overlap and cuts: 1,510 × 1.15 = 1,736.5 sq ft.
If you're ordering by squares (bundles of 100 sq ft), you need 18 squares. Our calculator does all of this instantly-but now you understand exactly what it's computing.
New Construction or Major Remodel
When you're building new or replacing all siding, accuracy is critical. You can't match existing siding colors and textures down the road if you order too little. Measure carefully: walk around the entire house and note the perimeter, account for architectural features like dormers or gables (these add height and area), and double-check all openings. If your house has complex geometry, break it into sections (front, back, each side) and calculate separately, then sum the totals.
Partial Replacement or Patch Work
If you're only re-siding one wall, a gable end, or a section of the house, the calculator still applies-just measure that specific area instead of the whole perimeter. This is handy when storm damage, rot, or age has affected only part of your exterior. You'll also want to order an extra 5-10% to match future repairs.
Vinyl vs. Fiber Cement vs. Wood
Each siding type has different waste factors. Vinyl siding is relatively forgiving—10% waste is usually enough. Fiber cement is more brittle and harder to cut accurately, so budget 15% waste. Wood shakes and shingles are labor-intensive to fit and overlap, requiring 15-20% waste. The calculator lets you select your material type and auto-adjusts the waste percentage, but knowing these differences helps you anticipate cost and labor time.
Mobile Home or Shed Siding
Smaller structures have higher waste percentages relative to area because you're making more cuts and seams per square foot. A 10' × 20' shed wall has way more corner and edge work than a 40' × 20' exterior wall. For small structures, add 20-25% to account for the cut-to-waste ratio. Our siding calculator includes a "small structure" adjustment for exactly this scenario.
Tips and Things to Watch Out For
Measure twice, order once. A measurement error of just one foot in perimeter on an average house translates to 20+ sq ft of siding. Walk around the house with a 100-foot tape, mark corners clearly, and verify your total.
Don't forget architectural features. Dormers, bay windows, roof overhangs that create alcoves, and gables add significant wall area. If your house isn't a simple rectangle, break it into shapes, calculate each separately, and add them together.
Account for gutter and soffit areas carefully. If you're replacing siding up to the gutter, measure to that line. If gutters and soffit stay, don't include them in your wall height. A 4-foot soffit overhang can change your net height by several feet if you measure wrong.
Openings are your friend-to a limit. Large window and door areas reduce siding material, but they also create sealing challenges. Make sure your calculator is subtracting openings, and budget extra for trim, flashing, and sealant around those edges.
Always order 10-15% more material than your calculation to account for waste, cuts, and breakage. On-site cutting, matching grain or texture, and unavoidable damage during delivery and installation mean some material becomes scrap. Better to have leftovers than to run short near the end.
Consider future repairs. If you're ordering siding now, some will inevitably be damaged over the years. Keep 2-3 extra pieces or a partial square in storage so you can patch it years later without re-ordering the entire product run.
Frequently Asked Questions
How do I measure my house perimeter?
Use a 100-foot tape or measure each side length individually and add them together. For a rectangular house, it's (length + width) × 2. Walk around the actual outside edge and account for jogs, bump-outs, and irregular shapes.
Do I subtract the entire window frame area or just the glass?
Subtract the entire frame opening (rough opening), not just the glass. The frame edges are also covered by siding, so include that area in your deduction. However, don't subtract the trim or flashing that sits on top of the siding-just the opening itself.
What if my house has a second story that's smaller than the first?
Measure each story separately and add the results. A Cape Cod or saltbox house with upper-story sidewalls that don't extend the full width needs careful attention. Calculate the first-story perimeter and height, then the second-story perimeter and height, subtract openings from each, and add them together.
Can I use this calculator for a garage or addition?
Absolutely. Measure the perimeter and height of the addition, subtract windows and doors, add waste, and you're done. If the addition is partially attached to the existing house, only measure the exposed walls-no need to side an interior wall where it connects to the main building.
How do I account for brick or stone siding?
Brick and stone are measured in individual units per square foot. Brick is roughly 5–7 pieces per sq ft (depending on brick size and joint spacing). The calculator has a brick/stone mode that converts square footage to brick or stone unit count. This also accounts for the mortar joint, which accounts for a small percentage of the installed area.
Should I add waste for siding I'm installing over existing siding?
Yes, add your standard waste percentage. Even if you're installing over old material, you're still cutting around openings, fitting at corners, and dealing with architectural breaks. The waste factor applies regardless of substrate.
What if I'm only re-siding a section of my house?
Use the calculator to measure just that section. If it's a single wall, perimeter is just that wall's length, and height is the wall height. If it's multiple walls, add their lengths to get the section perimeter, measure height, and proceed normally.
Related Calculators
If you're planning a larger exterior renovation, you'll probably need our roofing calculator (to estimate shingles or metal roofing for the roof slope), paint calculator (for trim and accent colors), and window size calculator (to verify rough openings for replacements). For a full material cost estimate, our material cost estimator lets you plug in your siding square footage and lumber prices to see the total project cost.