EstimatorKitFree siding and trim take-off
Siding calculator — squares, cartons and every stick of trim
Enter the wall runs, the gables and the openings, and this returns what a yard will actually sell you: squares of siding turned into cartons, boards or bundles, and then seven trim lines in linear feet — starter strip, J-channel, outside and inside corner posts, undersill trim, housewrap and flashing tape. A square of siding is 100 square feet of finished wall, vinyl arrives two squares to a carton, and every window you cut out takes area off the field while putting linear feet on to the trim. Two square counts come back rather than one — what the wall measures, and what it measures once your allowance is on it — because a yard sells in cartons and an installer bids in bare squares of wall.
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- 2 squares to a carton
- 7 trim lines
- Copies as a supplier list
A plain rectangle has four outside corners and none inside; every L, T or bumped-out wing adds two outside and one inside, or the other way about. Posts are the one line here you cannot cut from something else.
Boxed two squares at a time, so the purchase steps 200 ft² whether you need 5 ft² more or 195. Double 4 is an 8 in exposure, Dutch lap 9, double 5 is 10 — the profile changes how many panels come out of a carton, not how many cartons you carry home.
Why 15%: gables, dormers and a raked top course: every course that dies into a rake is cut on an angle, and an angled offcut starts nothing. The button fills the box below; type over it where your own offcut pile says otherwise.
Vinyl lap for 1,148 sq ft of wall
7 cartons
- Gross wall, gables in
- 1,420 sq ft
- Openings off
- −272 sq ft
- Squares, bare
- 11.5
- Squares, plus 15%
- 13.2
- Panels in those cartons
- 168 at 24 a carton
- Left in the last unit
- 79.8 sq ft
Vinyl steps 200 sq ft at a time — a carton of vinyl lap siding holds two squares — 200 ft² of finished wall, which profile: insulated panels and some premium lines ship one square to the carton. On a job needing 13.2 squares that step is worth more than the allowance is, so check the padded figure against the carton line before adding to it.
Trim, measured rather than guessed
| Starter strip136 lf along the bottom of every run — the course that every course above it copies | 11 sticks |
| J-channel173 lf of head and jamb over 13 openings, plus 62.6 lf up the rakes | 19 sticks |
| Outside corner posts10 ft covers a 9 ft corner in one piece, 1 ft over | 4 posts |
| Utility and undersill trim80 lf under the eave and 30 lf of window sill — everywhere a course is cut down and has nothing to lock into | 9 sticks |
| Housewrap1,420 sq ft gross, 1,578 sq ft once the laps are added | 2 rolls |
| Window flashing tape225 lf — all four sides of every opening, which is the one place the sill matters most | 3 rolls |
Sticks are counted at 12.5 ft lapped 0.75 in, so each one contributes 12.44 ft to the run once the lap is taken out — J-channel, starter strip and utility trim are stocked in 12 ft 6 in lengths, and it varies with supplier — 10 ft starter and 10 ft J-channel sit on the same rack. Posts use outside and inside corner posts are stocked in 10 ft, with 12 ft 6 in on most lines. Wrap rolls use a 9 ft by 100 ft roll of housewrap with 6 in of horizontal lap out of every 9 ft of roll height, 12 in at every vertical seam, and the wrap turned around each corner taken off it.
What the openings did to this order
13 openings took 272 sq ft off the field — 2.72 squares — and put 203 linear feet of channel and trim on to the order, while leaving the housewrap exactly where it was. That is a small enough deduction that rounding it away and letting the allowance absorb it would barely show, and it is still worth entering, because the trim it generates would not be absorbed by anything. The biggest single opening here is 112 sq ft, so it deducts like a small wall and trims like one too — a garage opening is usually the largest single line of J-channel on a house. Against 13.2 squares of field material this job carries 481 feet of accessory, or 36.5 feet a square.
How to take off siding and its trim
Runs and gables for the area, openings for both directions, then one decision about waste.
Enter wall runs, not a perimeter
Give each run its length at the base, its height to the plate, and how many walls the building has that size — two 40 ft sides and two 28 ft ends is two rows, not four. The base length is doing two jobs at once: it is half the area and it is every foot of starter strip on the job. Gables go in on their own line as a width at the plate and a rise to the peak, because a triangle is half its base times its rise and because its two sloping edges are a length the wall below it never tells you.
List the openings by size and say which ones have a sill
One row per size with a count beside it: ten identical windows is a single row, and a garage door is its own row because 112 square feet behaves nothing like 12. Tick the sill box for a window, leave it clear for a door or a garage opening whose bottom edge meets a threshold. That one box decides where the bottom of the opening sends its linear feet — a window sill takes undersill trim, a door bottom takes nothing at all, and both take J-channel across the head and down each jamb.
Choose the material, set the allowance, then read both totals
Vinyl comes back in cartons, because that is the only quantity a yard will sell you: a carton is two squares whether you are 5 square feet short of one or 195. Fiber cement, engineered wood and cedar come back as boards and bundles at whatever exposure you nail to. Two square counts are printed rather than one — what the geometry says, and what the geometry says plus your allowance — because the allowance is a purchasing decision and the measurement is not. Buy on the second number and check anyone else's takeoff against the first.
Technical specifications
| Wall input | Any number of runs, each a length, a height and a count, plus gables as width at the plate and rise to the peak. 28, 28' 6", 340 in and 8.7 m all parse |
|---|---|
| Openings | One row per size with a count and a sill flag: deducted from the field, added to the J-channel, ignored by the housewrap |
| Materials | Vinyl lap at 2 squares a carton, fiber cement at a 7 in exposure on 12 ft boards, engineered wood at 6 3/4 in on 16 ft, cedar shingles at 4 bundles a square |
| Exposure | 2 to 16 in, moving the piece count without moving the square count — a double 5 profile and a double 4 buy the same number of cartons |
| Allowance presets | 10% plain, 15% gabled, 20% cut up, plus 5 points for shakes; the preset fills a percent box you can type straight over |
| Trim lines | Seven: starter strip, J-channel, outside posts, inside posts, undersill trim, housewrap, flashing tape |
| Accessory sticks | 12 ft 6 in with a 3/4 in lap, leaving 12.44 ft of usable run per stick; corner posts 10 ft and 12 ft 6 in, counted uncut |
| Data kept | None. Reloading the page brings back the sample house, not the building you just measured |
Frequently asked questions
How many boxes of vinyl siding do I need?
Divide the net wall area by 200 square feet and round up, because a carton of vinyl lap holds two squares and a square is 100 square feet. A 1,148 square foot wall with a 10% allowance is 12.6 squares, which is seven cartons — 1,400 square feet delivered for 1,263 needed. That 200 square foot step is bigger than the waste allowance on most single-elevation jobs, so settle the allowance first and let the carton rounding be the last thing that happens, rather than padding a number that is about to be rounded up anyway. Insulated panels are the exception worth checking on the ticket: most of those ship one square to the carton, not two.
Do I subtract windows and doors from the siding?
Yes from the field material, and from nothing else on the order. An opening takes its own area off the siding and simultaneously adds its head and both jambs to the J-channel, so a 3 by 4 window removes 12 square feet of panel and adds 11 feet of channel. The housewrap does not move at all, because wrap is run straight across the opening and cut out afterwards with an I-cut so the flaps can be folded into the jamb — which makes it the one line on this page a window never shrinks. Estimators who skip small openings are half right: the deduction genuinely is trivial, and the trim it generates is not.
How much J-channel does a window take?
Its width plus twice its height — head and both jambs — so a 3 by 4 window is 11 feet and ten of them is 110 feet, which is nine sticks at 12 ft 6 in. The sill is the exception: most installs put undersill trim under the sill rather than J, because the course beneath a window is cut down and needs somewhere to lock, and this page routes it there whenever the sill box is ticked. Then add the rakes. J-channel runs up both sloping edges of every gable, and a rake is always longer than the wall underneath it is wide — a 28 foot gable with a 7 foot rise is 15.7 feet of rake per side, 31.3 feet for the gable and 62.6 for a pair of gable ends, which is more channel than five 3 by 4 windows take between them.
Can a corner post be cut and spliced?
It can, and it shows, which is why the answer to a tall corner is a longer post rather than a joint. The splice itself is prescribed: cut an inch off the nailing flanges of the upper post, lap it 3/4 inch over the lower one so water sheds outward, and the seam still catches the light across a flat wall. Stocked lengths are 10 ft and, on most lines, 12 ft 6 in — enough for any single story. A two-story corner needs either a 20 foot post from a line that makes one, or a deliberate splice placed at the floor band where the eye already expects a horizontal break, never at eye level in the middle of a wall.
Why does the starter strip matter more than any other stick on the wall?
Because every course above it is a copy of it. The first panel locks into the starter, the second locks into the first, and nothing further up ever gets a chance to correct an error introduced at the bottom — the wall arrives at the soffit carrying exactly the error it left the ground with, and the soffit line is dead level, so the discrepancy shows as a wedge of daylight along the top course. Snap a level line right round the building before a single stick goes on, keep it low enough that the first course covers the top of the foundation, and keep it high enough that untreated wood siding sits 6 inches above grade and 2 inches above a concrete step or walk, which is what IRC R317.1 asks for.
How much waste should I allow on siding?
Ten percent on a plain rectangular elevation, 15% where there are gables or dormers, 20% where bays and returns break the wall into short runs, and five points more again for shakes and shingles, which are culled at the wall for width and grade. What drives it is the angle of the cut rather than the size of the job: on a long straight wall the offcut from the end of one course is the start of the next and almost nothing is thrown away, while every course that dies into a rake is cut on an angle and its offcut begins nothing. The worst case is a wall shorter than a single panel, where every course produces a dead end and the loss can pass 20% on a shape with no gables at all.
How many rolls of housewrap does a house take?
One 9 by 100 foot roll covers 900 square feet before laps, so a 1,400 square foot wall takes two. Count it against the gross wall with the openings still in it, add roughly a tenth for the laps — 6 inches horizontally out of every 9 feet of roll height, a foot at every vertical seam, plus the length turned around each corner — and buy flashing tape separately for the openings, at four sides each rather than three. Order of work decides how much of it survives: wrap goes on before any trim, the openings are cut and flashed, and only then does the starter strip get snapped, which is why a roll count worked out after the trim is on is always short.
About buying siding by the square and trimming it by the foot
Siding is sold in squares — 100 square feet, the same unit the roofing calculator uses for the roof over it — and vinyl lap is boxed two squares at a time, which makes 200 square feet the smallest amount of wall anybody can buy. That step is the first thing most estimates get wrong, because it is usually larger than the waste allowance being argued about: a wall needing 12.6 squares and a wall needing 13.9 both leave the yard as seven cartons. Exposure is the second. A double 4 profile lays two 4 inch courses per panel and a double 5 lays two 5 inch ones, so the panel count out of the carton drops from 24 to 19 — and the carton count does not change at all, because coverage is coverage. It matters for the lap boards instead: an 8 1/4 inch fiber cement plank lapped 1 1/4 inches leaves a 7 inch exposure and covers 7 square feet on a 12 foot length, and nailing to a 6 inch exposure instead is a sixth more boards for the same wall. Course exposure is the wall’s version of the same question the shingle calculator answers for the roof.
The trim is the half this page exists for, and the half that never appears in a perimeter-times-height estimate. Six items are measured along edges, not across a surface. Starter strip runs the full base of every wall, and it is the most consequential stick on the job: every course locks into the one below it, so the whole elevation inherits whatever the starter did, and an error that would be invisible at the ground arrives at a dead-level soffit as a visible wedge. J-channel goes across the head and down both jambs of every opening, and up both rakes of every gable — which is why the form asks for the gable rise rather than its area alone: a 28 foot gable with a 7 foot rise carries 15.7 feet of rake on each side, 31.3 feet for the gable, and if you know the roof as a pitch instead of a rise, the roof pitch calculator converts it. Corner posts are counted, not measured: one per corner per story, bought at a length that covers the corner in a single piece, because the prescribed splice — flanges cut back an inch, upper lapped 3/4 inch over lower — is watertight and still catches the light. Undersill trim picks up every course that has been cut down and has nothing left to lock into: the top course under the eave, and the course beneath each window sill.
Two things about a wall have no equivalent on a roof, and both are worth knowing before the first panel goes up. Vinyl is hung rather than fastened: a 12 ft 6 in panel moves about half an inch across a 100 °F swing between a February morning and an August afternoon, so nails go in the center of the slot, are left about 1/32 inch loose under the head, and the panel is cut a quarter inch short at each end so it has somewhere to go. A panel nailed tight buckles in the first heatwave and there is no fixing it short of taking the wall off. The other is the ground. Untreated wood siding has to finish 6 inches above grade and 2 inches above a concrete step, porch or walk under IRC R317.1, which is a clearance a landscaper can quietly destroy years later by raising a bed against the wall — and if the walk itself is still ahead of you, the concrete calculator sizes that pour. Neither of these is arithmetic, which is precisely why the calculators that hand back a square count and stop have nothing to say about them.
What leaves this page
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The dimensions of one specific building are close to an address, and they are treated like every other number here: read as you type them, and gone with the tab. No lead form wears a calculator’s clothes on this page — the Copy button writes a plain-text list to your clipboard, and that is the end of it.