A siding estimate should carry separate lines for tear-off and disposal, house wrap and flashing, the siding itself in squares, trim and accessories, fasteners and sealant, labour, and an allowance for hidden damage. To find squares, multiply each wall's width by its height, add gables, subtract openings, add a waste percentage, then divide by 100.
Waste is a judgement call, so give it its own visible line instead of burying it in a unit price. Use ChatGPT for the second pass, asking what is missing from a finished estimate, and keep the arithmetic in a spreadsheet, because chat assistants slip on long sums.
The lines a siding estimate needs, in the order a crew works
Order the lines the way the job happens, because a reviewer reads top to bottom and an out-of-order estimate hides gaps. The table gives each line, the unit, how the quantity is found and the detail that goes missing most often.
| Line | Unit | How the quantity is found | Easy to forget |
|---|---|---|---|
| Access and protection | Allowance | Ladder or scaffold days, ground sheets, covers | Protecting shrubs, windows and air-conditioning units |
| Tear-off and disposal | Squares, plus one haul | Net wall area divided by 100 | A second layer of old siding, and the disposal fee |
| Hidden-damage allowance | Rate per sheet | Unit rate only, billed if found and approved | Writing it as a rate, outside the total |
| House wrap and seam tape | Rolls | Gross wall area plus laps, divided by roll coverage | Gable ends, and wrap behind the openings |
| Window and door flashing | Linear feet | Opening perimeters | Sill and head details are more than tape |
| Starter strip | Linear feet | Perimeter minus door widths | Starting course on bump-outs |
| Siding | Squares or pieces | Net area times one plus waste | Waste kept on this line only |
| Corners | Linear feet | Corner count times wall height | Inside corners on bump-outs |
| Window, door and rake trim | Linear feet | Opening perimeters and gable edge lengths | Rake trim on gables |
| Fasteners, sealant, touch-up | Allowance | Per square or lump sum | Colour-matched sealant and nails |
| Fixtures removed and refitted | Each | Count on the site visit | Lights, hose taps, vents, meter boxes |
| Painting or priming | Squares or linear feet | Only if the product is painted on site | Two coats, and the trim |
| Labour | Installed squares | Net area divided by 100 | Pricing labour on ordered squares by mistake |
| Permit and inspection | Allowance | Only where one is needed | Who pays, in writing |
| Overhead, profit, contingency | Percentage | Applied to the subtotal | Stating the percentage you used |
Two rules keep the table honest. Waste lives on the siding line only, and labour is priced on installed squares, not ordered squares, because the crew is not paid to install the offcuts.
From wall measurements to squares: one house, step by step
Take an illustrative two-storey house, 40 ft by 26 ft on plan, with 18 ft of wall height and a gable on each short side rising 8 ft to the peak. Every figure here is made up to show the method. If you work in metres, the method is identical: a square is 100 square feet, or about 9.3 square metres.
| Step | Working | Result |
|---|---|---|
| 1. Perimeter walls | (40 + 26) x 2 = 132 ft, times 18 ft | 2,376 sq ft |
| 2. Gables | Two triangles, half of 26 ft times 8 ft each | 208 sq ft |
| 3. Gross area | 2,376 + 208 | 2,584 sq ft |
| 4. Openings | 12 windows at 3 x 5 ft (180), 2 picture windows at 6 x 5 ft (60), 2 entry doors at 3 x 7 ft (42), 1 patio door at 6 x 7 ft (42) | 324 sq ft |
| 5. Net area | 2,584 - 324 | 2,260 sq ft, or 22.6 squares |
| 6. Add 12% waste | 2,260 x 1.12 | 2,531 sq ft, or 25.3 squares |
| 7. Order | Round up to whole squares | 26 squares |
Steps 1 to 5 give the area the crew installs, so tear-off and labour use 22.6 squares. Steps 6 and 7 give the area you buy. That split is the reason for keeping waste on its own line.
If the siding is sold by the piece, convert coverage first. A lap plank 12 ft long that shows 7 inches once installed covers 12 x 7/12 = 7 sq ft. Take the exposure from the product's data sheet, not from this example. Then 2,531 divided by 7 is 361.6, so order 362 planks.
Some suppliers quote by the face area of the board instead of its coverage. In that case divide the wall area by the ratio of exposure to width: an 8 inch board showing 6 inches covers 75% of its face, so 100 sq ft of wall needs about 133 sq ft of board. Ask which basis a quote uses before comparing two suppliers, because the same house gives two different numbers.
The Complete Excel Course with AI Integration
From formulas and pivot tables to Power Query, DAX, VBA and AI with Copilot, ChatGPT and Claude — hands-on from the first lesson.
By Sagnik Bhattacharya and Virginia Thorn, Primetime Emmy Award winner
Buy nowChoosing a waste percentage you can defend
Waste differs by wall shape, material and crew. Online siding calculators commonly suggest adding 5% to 10%, with more for complicated walls, and the right figure for you is whatever your own jobs show. Start from the table below and replace it once you have five jobs of your own.
| Wall shape | Starting waste | Reason |
|---|---|---|
| Plain single storey, few openings | 8% | Long runs, few cuts, offcuts reusable |
| Two storeys, gables and a dozen or more openings (the example) | 12% | Many end cuts around openings and along gable edges |
| Dormers, bays, turrets, diagonal or patterned runs | 15% or more | Small pieces, angled cuts, little offcut reuse |
Two quick sums show the effect. A single-storey bungalow with 1,100 net sq ft at 8% needs 1,188 sq ft, which is 11.9 squares, so order 12. A complex house with 1,800 net sq ft at 15% needs 2,070 sq ft, or 20.7 squares, so order 21. The same method gives a waste allowance of 0.88 squares on the bungalow and 2.7 squares on the complex house.
To find your own number, write down three figures after each job: squares delivered, squares returned unopened, and squares installed. Scrap is delivered minus returned minus installed. For the example house, say 26 delivered, 0.5 returned and 22.6 installed: scrap is 2.9 squares, and 2.9 divided by 22.6 is 12.8%. That is close to the 12% allowed, so the allowance stays. After five jobs of one house type, the average becomes your defensible figure.
Waste also moves with the material, so check the manufacturer's installation guide for cutting, lap and joint rules before you settle on a number for a new product. If you price roofs as well, the squares-and-waste habit carries over, and roofing takeoff with AI shows the same sums for bundles.
Counting trim, corners and flashing in linear feet
Linear lines come from the opening list and the corner count, and they get their own, smaller waste allowance. First the perimeters: a 3 x 5 ft window is 2 x (3 + 5) = 16 ft, a 6 x 5 ft picture window is 22 ft, an entry door needs a head and two sides, 3 + 7 + 7 = 17 ft, and the patio door is 6 + 7 + 7 = 20 ft. Each gable edge runs along the hypotenuse of a triangle with a 13 ft half-base and an 8 ft rise, which is about 15.3 ft, and there are four such edges.
| Item | Working | Feet | With 10% waste | Pieces at 12 ft |
|---|---|---|---|---|
| Outside corners | 4 corners x 18 ft | 72 | 80 | Cut to length; check what lengths are sold |
| Window and door trim | 12 x 16 + 2 x 22 + 2 x 17 + 20 | 290 | 319 | 27 |
| Rake trim on gables | 4 edges x 15.3 ft | 61 | 67 | 6 |
| Starter strip | 132 ft perimeter minus 12 ft of door widths | 120 | 132 | 11 |
| Flashing tape at openings | Same perimeters as trim | 290 | 319 | By roll length |
Round pieces up, never down: 319 divided by 12 is 26.6, so 27 pieces. Check the lengths your supplier actually stocks, because 10 ft or 16 ft pieces change the count and the offcut pattern. If a bump-out adds two inside corners, they belong on this table as their own row with their own feet.
House wrap and tear-off: the two lines short estimates drop
House wrap covers the whole wall, openings included, so it is counted from gross area: 2,584 sq ft here. Add an allowance for laps and cuts, 15% in this example, which gives 2,972 sq ft. With rolls 9 ft wide and 100 ft long, 900 sq ft each (one of several standard sizes on a major house-wrap maker's product page), 2,972 divided by 900 is 3.3, so four rolls. Check your product's roll size and the lap rules in its installation instructions, then replace both assumptions.
Tear-off uses the net squares, 22.6, plus one disposal charge. Two questions at the site visit change this line more than any unit price. First, is there a second layer under the first? Second, might the old cladding or paint contain hazardous material? Older siding and paint can contain asbestos or lead. If you suspect either, stop, arrange testing before you price a tear-off, follow the rules that apply to your work, and write the answer on the estimate.
Write what you found next to the line, for example "one layer of existing siding, no suspect material seen, customer told testing is not included". A sentence like that costs nothing and prevents an argument at the end of the job.
Pricing the lines: the estimate page, with made-up unit prices
The next table puts the quantities from the sums above onto a priced estimate. The unit prices are round figures invented for this illustration, not market rates, so replace them with your supplier invoices and your own labour rates.
| Line | Quantity | Unit | Unit price | Total |
|---|---|---|---|---|
| Tear-off of existing siding, labour | 22.6 | squares | $55.00 | $1,243.00 |
| Container and disposal | 1 | each | $450.00 | $450.00 |
| House wrap, 900 sq ft rolls | 4 | rolls | $165.00 | $660.00 |
| Flashing tape, windows and doors | 319 | ft | $0.60 | $191.40 |
| Lap siding planks, 12 ft | 362 | pieces | $13.50 | $4,887.00 |
| Starter strip, 12 ft | 11 | pieces | $6.00 | $66.00 |
| Outside corner trim | 80 | ft | $4.20 | $336.00 |
| Window and door trim | 319 | ft | $2.10 | $669.90 |
| Rake trim | 67 | ft | $2.10 | $140.70 |
| Fasteners, sealant, touch-up kit | 1 | allowance | $240.00 | $240.00 |
| Installation labour, net squares | 22.6 | squares | $210.00 | $4,746.00 |
| Subtotal | $13,630.00 | |||
| Overhead and profit at 20% | $2,726.00 | |||
| Estimate total | $16,356.00 |
The total works out at $723.72 per net square, a number worth tracking across jobs because it shows quickly when one estimate is out of line with the rest. The waste is visible too: the house needs 323 planks (2,260 divided by 7), the order is 362, so 39 planks or $526.50 of material is waste. Showing that figure to the customer is optional. Showing it to yourself is not.
Asking ChatGPT what is missing, and what to fix in its answer
The second pass is where the assistant earns its place. Paste in the finished line table and the wall measurements, and ask for omissions and inconsistencies, never for new totals.
You are reviewing a siding estimate for a two-storey house before it goes to the customer. Below are my estimate lines and my measurements.
Do not recalculate totals.
List: (1) items normally part of a siding job that are not on my estimate; (2) lines whose quantity looks inconsistent with my measurements; (3) exclusions I should state.
Tag each item as ADD A LINE, CHECK ON SITE or ASK THE CUSTOMER. If you are unsure, say so instead of guessing.An illustrative reply, trimmed to the points that matter:
- Add a line: sill flashing or sill pans at the windows. Your list has flashing tape only.
- Check on site: exterior lights, hose taps and vents on the walls. Removal and refitting are not listed.
- Ask the customer: siding colour and profile, trim material and whether trim is painted on site.
- Add a line: permit and inspection fee.
- Inconsistent: your 12% waste looks high against a typical 5%.
- Exclusions: painting, hidden damage beyond the allowance, hazardous-material testing.
Now the fixing. Adopt the first two points: they are real omissions, and sill flashing is the sort of item that disappears from an estimate until a window leaks. Keep the third as a question for the site visit. Drop the permit line unless your work requires one. Ignore the waste comment: the "typical 5%" came from nowhere you can check, and your own records beat it. Tell the assistant to stop commenting on waste too, because it may otherwise repeat the point on the next run.
Finally, the assistant missed the hidden-damage allowance wording, which only you know to ask for, so write that line by hand: "Sheathing repair, if found, at $X per sheet, billed only with the customer's written approval." Treat the output as a prompt for your own judgement, a list of things to check rather than a list of answers. For a longer version of this pass on another job type, see how to catch missing lines in a bathroom remodel estimate.
Scope and exclusion wording the customer will actually read
Customers read the scope lines more closely than the prices, and disputes start in the gap between what they assumed and what the line said. Three rewrites show the difference.
- Before: "Siding: $14,200." After: "Remove existing siding from all four walls and both gables (about 22.6 squares) and dispose of it. Install house wrap, flashing tape at 14 windows and 3 doors, and new lap siding in the profile and colour agreed."
- Before: "Allow for waste." After: "Material is ordered with an allowance for cuts; unopened full boxes at the end of the job are returned for credit." (Say this only if it is true for your supplier.)
- Before: "Extras if needed." After: "If rotten or damaged sheathing is found when the old siding is removed, it will be replaced at $X per sheet only after your written approval."
To turn your own shorthand into lines like these, give the assistant one rough line and a reading level.
Rewrite this estimate line in plain English for a homeowner, in two sentences, saying exactly what is included. Do not add anything that is not in my text, and put a question mark after anything you had to assume: "R+R siding all elevs, 22.6 sq, wrap, tape, lap plank, trim to openings".The question-mark instruction is what makes this safe. Every question mark in the reply is a fact you must confirm before the line goes out. For the standing exclusions, a short list covers most disputes: painting, hidden damage beyond the allowance, testing or removal of hazardous materials, repairs to landscaping and fences damaged by access, and any electrical or plumbing work beyond removing and refitting fixtures.
The mistake that cost two squares
An invented case of the same slip: a three-person siding crew priced a two-storey house from ground-level wall lengths and heights and left out the gable triangles. The gables in the example above come to 208 sq ft, just over two squares, so the crew ran out of siding at the second wall's peak. The reorder came from a different production batch, and the shade differed slightly where the new boxes met the old.
The cost was a half-day of waiting and a conversation with the customer about the colour join. The fix was boring and effective: gables became their own line on the measurement sheet, and "gables included: yes or no" became the first tick on the pre-send check below.
Five checks before the estimate goes out
- The squares reconcile. Gross minus openings gives net; net times one plus waste, divided by 100, gives the order. Re-add it in a spreadsheet, not in your head and not in the chat.
- Every opening appears twice. Once in the area deductions, and once in the trim and flashing lines. An opening in only one place is a missed or a doubled count.
- Gables are in. Tick it, as above.
- Waste is on the siding line only. Tear-off and labour use net squares, and the waste figure has a stated percentage.
- Allowances and exclusions are written. Hidden damage has a unit rate, and hazardous-material testing is either included or excluded in so many words.
If you are choosing software to hold these lines, siding contractor software covers what to pay for, and if measuring the walls is the slow step, the six AI takeoff tools matched to trade and plan type include two that measure exteriors from photos or aerial images. The arithmetic in the chat window is the weakest part of the whole process, so read why AI is bad at maths before you rely on any total it gives you, and see demolition estimate lines for scope, waste and disposal if your tear-off work is large.
Siding estimate questions that come up on site
How many squares of siding do I need for a house?
Measure each wall's width and height, add the gable triangles, subtract windows and doors, add your waste percentage and divide by 100. The two-storey example in this tutorial comes to 22.6 net squares and 26 ordered at 12% waste. Houses differ, so always run your own sums.
Do I subtract windows and doors when estimating siding?
Most estimators do for large openings, because no siding goes there. Some leave small openings in as extra allowance. Pick one rule, apply it to every estimate, and write it on the estimate so a reviewer or customer can see how the squares were found.
Can ChatGPT calculate siding squares for me?
It can set out the method and spot missing items, but long sums are where chat assistants slip. Do the arithmetic in a spreadsheet, paste the finished table in, and ask the assistant to check it against your wall list rather than to produce the total.
What waste percentage should I use for siding?
There is no single correct figure. Online siding calculators commonly suggest adding 5% to 10%, and walls with gables, dormers and many openings need more, so treat that as a starting point. Record delivered, returned and scrapped material on five jobs and use your own average.
Should hidden damage be priced into the estimate?
Not as a fixed number, because nobody knows until the old siding is off. Add an allowance line with a unit rate, for example per sheet of sheathing replaced, and state that it is billed only if found and approved. That protects both sides.
Further reads
- Gutter Quote Template: Run Lengths and Downpipes Priced With AI — Another linear-feet quote: gutter runs and downpipes priced with AI.
- Plastering Quote Template: Skim, Render and Patch Lines With AI — A wall-finish quote template with patch and render lines.
- Roofr vs EagleView vs Hover: AI Roof Reports, Cost per Job, Turnaround — Roof reports compared on cost per job and turnaround.
- Concrete Estimate Template: Volume, Pump and Finishing Lines With AI — The same worked-sums approach applied to concrete volumes.
- Masonry Takeoff With AI: Counting Bricks and Blocks From an Elevation — Counting bricks and blocks from an elevation drawing.
- Follow Up After Giving a Quote: An HVAC Replacement Sequence With AI — What to send after the estimate has gone out.
- How to Quote Scaffolding: Elevations, Boards and Hire Periods With AI — A worked wrap-around quote: elevation areas, lifts, boards, erect and dismantle labour, weekly hire and extras, with an AI check that the sum reconciles.
- Landscaping Estimate Template: Itemise Labour, Plants and Waste With AI — A worked front-garden estimate with labour, plant, materials and waste lines, a margin check, and four AI prompts that do the typing, not the pricing.
- AI Tools and AI Development: The Complete 2026 Guide — the AI hub, including every tutorial in the AI-for-business series.
Sources: standard wall-area and squares arithmetic; an online siding calculator's waste guidance and a house-wrap maker's roll-size table, read 1 November 2026; your siding and house-wrap manufacturers' installation instructions for coverage, laps and fastening. All unit prices in the worked estimate are made-up round figures, not market rates.