# Siding Calculator > Free siding calculator: work out net wall area, squares, panels or boxes and the trim you buy — starter strip, J-channel and corner posts. Vinyl lap, fiber-cement, board & batten or shakes, gable walls, openings deducted, metric or imperial, in your browser. Net wall area → squares, panels or boxes and the trim you buy — go wall by wall, deduct openings, pick a profile, and read a live shopping list in your browser. - **HTML page:** https://siteometry.com/en/tools/siding-calculator - **Category:** [Roofing & Siding](https://siteometry.com/en/tools/category/roofing-siding) - **Figures live on the page:** tables, diagrams and worked figures the text refers to ("the table below") are drawn by the page and are not reproduced here. Each section below links to its anchor on the page. - **Runs in the browser:** Siteometry calculators need no account and send no input anywhere — every number below is computed on the visitor's own device. ## How to estimate siding and trim in 5 steps 1. **Choose units** — Select metric (m, m², mm, squares as m²) or imperial (ft, ft², inches, squares) at the top of the page. Terminology and default sizes follow your choice. 2. **Pick a profile** — Open Assumptions & materials and choose a siding profile — vinyl lap, horizontal or vertical panel, fiber-cement lap, board & batten or shakes. Override its exposure, panel length or coverage if your product differs. 3. **Add walls** — Add a wall for each face. Set the shape (rectangle or gable), enter the dimensions or a known area, and add door and window openings to deduct from the net area. 4. **Set waste and accessories** — Choose a waste allowance (10%, 15% or your own) and, in dimensions mode, the number of outside and inside corners plus the corner height and per-wall starter, J-channel and trim toggles. 5. **Read the results** — The Results panel shows the squares, field panels or boxes, and starter, J-channel, corner-post and trim lengths to buy — add prices for a material total and cost per square. _On the page: https://siteometry.com/en/tools/siding-calculator#howto_ ## Siding & Cladding Calculator Cladding a house means buying the right amount of siding first time — the field material measured in squares, panels, boards or boxes, and the linear trim that goes with it: starter strip, J-channel, inside and outside corner posts and finish trim. Order short on the trim and you stop mid-run for another trip; order long and you are left with stock lengths you cannot return. This calculator takes each wall — rectangle or gable, dimensions or a known area — deducts its doors and windows, and turns the net area into squares and a piece count for the profile you pick. It then runs a separate accessory pass over the wall bottoms, opening perimeters, corners and rake edges to size the trim in the lengths it is sold in. Add prices for a rough cost, and read a live shopping list. Everything runs in your browser. Switch between metric and imperial at any time. Walls, gable rise and stock lengths follow the unit; exposure and panel width are shown in millimetres or inches; and the headline reads in squares in imperial or square metres in metric. There is no separate region selector — the terminology and default sizes follow the unit switch. _On the page: https://siteometry.com/en/tools/siding-calculator#guide-intro_ ## How many squares of siding do you need? Siding is measured in squares, exactly as roofing is: one square is 100 square feet (9.29 m²) of finished wall. The count is area-based. For each wall the calculator works out the net area — the wall area minus any openings — and adds it into a project total, which it divides by 9.29 m² to give squares. A gable wall folds its triangle above the eave into the same net area. Because the headline comes from area, the profile you choose does not change the squares — only how those squares turn into panels, boards or bundles. The figure below is a whole gable-end wall with a door and two windows cut out, drawn in lap coursing with its starter strip, corner posts and rake J-channel marked. _On the page: https://siteometry.com/en/tools/siding-calculator#how-many-squares_ ## From squares to panels, boards and boxes The profile decides how the net area becomes a piece count, because different products are sold by genuinely different units. The calculator groups every profile into one of three piece-math families, so the same net area gives the right count whichever you pick. Horizontal lap and panel profiles sell by the board, whose coverage is its length times its exposure (reveal). Vertical and board-and-batten profiles sell by the panel, whose coverage is its width times its length with no overlap. Shakes sell by the bundle at a fixed coverage — four bundles make a square. Vinyl lap additionally comes boxed, roughly two squares to a box, so the calculator shows both loose panels and boxes to buy. Every quantity is rounded up across the whole project so partial walls share a box or a board rather than each rounding up alone. _On the page: https://siteometry.com/en/tools/siding-calculator#how-many-boxes-pieces_ ## How to use the siding calculator Choose metric or imperial units at the top; the calculator remembers your choice in your browser and follows it for terminology and default sizes. Open the Assumptions & materials card to pick a siding profile and, if you want, override its exposure or reveal, board or panel length, waste allowance and accessory stock lengths. In per-wall dimensions mode you also set the number of outside and inside corners and the corner height. Every constant the calculator uses is shown here and can be edited to match your product spec. Add a wall for each face of the house. Set the shape — rectangle or gable — enter the dimensions or a known area, and add door and window openings to deduct. Each wall shows its own net area and pieces; the Results panel accumulates every wall into project totals: squares, field panels or boxes, and a starter, J-channel, corner-post and trim shopping list. _On the page: https://siteometry.com/en/tools/siding-calculator#how-it-works_ ## Siding profiles and how they change the count Vinyl lap comes as double-course panels twelve feet long in three common reveals — Double-4 (8″ exposure, about 8 sq ft a panel), the standard Double-4.5 (9″, about 9 sq ft) and Double-5 (10″, about 10 sq ft). Horizontal panel is a plain single-course version of the same lap math. Fiber-cement lap, such as HardiePlank, is a twelve-foot board with a typical 7″ exposure at the common 8¼″ width. Board-and-batten and vertical panel run as full-height columns, sized by panel width rather than exposure — an 8″ default here, with no course overlap. Shakes and shingles are estimated by the bundle at a 5½″ exposure, where four bundles cover a square. Picking a profile loads its exposure and coverage defaults, all of which you can override; the squares stay the same, but the piece count and the diagram coursing change. _On the page: https://siteometry.com/en/tools/siding-calculator#profiles_ ## Accessories: starter, J-channel, corners and trim The trim is where a bare area calculator sends you home short. Siding accessories are linear, not area-based, so the calculator runs a separate pass over the job's geometry and rounds each total up to the lengths it is sold in — starter strip in 10 or 12 ft, J-channel in 12½ ft, corner posts in 10 ft, or metric stock lengths in metric. This pass needs real wall geometry, so it runs only in per-wall dimensions mode. In area-only mode the calculator still gives you squares and a field-panel count, but no accessory list, because a single area figure carries no bottoms, corners or opening perimeters to measure. The map below shows what each accessory is and where it goes. _On the page: https://siteometry.com/en/tools/siding-calculator#accessories_ ## How much waste should you add? Waste covers the offcuts you cannot avoid: the panel cut around a window, the angled scrap along a gable rake, the piece snapped on site. The calculator adds it to the field piece count before rounding up to whole panels, boards or bundles. Ten percent suits straightforward walls with few openings. Fifteen percent is a safer allowance for gable-heavy jobs and lots of cut-outs, where the raked cuts waste more of each course; decorative and shake work can run to twenty. Use the quick picks or type your own percentage — the override wins whenever it is a valid number. When a wall is a gable, the tool nudges you toward the higher allowance. _On the page: https://siteometry.com/en/tools/siding-calculator#waste_ ## Worked examples Three quick takeoffs at the default coverage and stock sizes. Your own numbers will differ once you set the profile, exposure and waste to your spec, but these show how net area, squares, pieces and accessories come together. _On the page: https://siteometry.com/en/tools/siding-calculator#worked-examples_ ## Common mistakes to avoid Confusing the drawn courses with the buy count. The diagram is a schematic that lays representative courses across the wall; the number to buy is higher because it includes your waste allowance and rounds up to whole panels. Always order from the Results panel, not by counting courses in the figure. Skipping the accessory takeoff, or expecting it in area mode. Starter strip, J-channel and corner posts are what a bare square count leaves out, and they only compute from per-wall dimensions. If you enter a single total area you will get squares and panels but no trim list — switch to dimensions to size the accessories. Trusting one brand's coverage everywhere. Exposures, panel widths and box counts vary by manufacturer and product line, so a default that suits one vinyl line can be wrong for another. Confirm the exposure and pack sizes against your supplier's spec and override the defaults before you order. _On the page: https://siteometry.com/en/tools/siding-calculator#common-mistakes_ ## Frequently asked questions ### How much siding do I need? Work out the net area of each wall — length times height, plus the gable triangle, minus doors and windows — add it up, and divide by 100 sq ft (9.29 m²) to get squares. Then divide the net area by your profile's coverage per piece and add waste to get panels, boards or bundles. The calculator does this for every wall and totals it, and also sizes the starter, J-channel and corner-post trim from the wall geometry. ### What is a square of siding? A square is 100 square feet (9.29 m²) of finished wall — the same trade unit roofing uses. It is the headline the calculator leads with in imperial, with square metres in metric, and it is shown alongside the panel or box count so you can cross-check. Squares depend only on net area, not on which profile you pick. ### How many boxes or pieces of vinyl siding is that? Vinyl lap is sold both loose and boxed, roughly two squares (about 200 sq ft) to a box, so the calculator shows panels and boxes to buy. A box typically holds 14–25 panels depending on the panel size, so treat the box figure as a guide and confirm the pack contents with your supplier. Other profiles are counted as loose boards, panels or bundles. ### How is the piece count worked out? It is area-based per profile family: pieces = ceil(netArea ÷ coveragePerPiece × (1 + waste)). Coverage per piece is a board's length times its exposure for lap and panel, the panel width times its length for vertical, or a fixed bundle coverage for shakes. The count is rounded up across the whole project, so leftover coverage from one wall carries into the next. ### How much starter strip and J-channel do I need? Starter strip is the sum of the wall bottoms that start siding at the foundation, rounded up to 10 or 12 ft stock. J-channel is the sum of the opening perimeters — count × 2 × (width + height) for each door and window — plus any top and rake edges you flag, rounded up to 12½ ft stock. Both are computed from per-wall dimensions, so they are only available in dimensions mode. ### How many corner posts do I need? Corner posts run the full height at each external and internal corner of the house. Because independent wall faces carry no adjacency, the calculator seeds four outside corners and zero inside once you have two or more walls, and you adjust the counts to your footprint. Each corner takes its own post, so the calculator rounds the corner height up to 10 ft stock and then multiplies by the number of corners. Leave the corner height blank to default to your tallest wall. ### How much waste should I add? Ten percent suits straightforward walls with few openings. Fifteen is safer for gable-heavy jobs and lots of cut-outs, where the raked cuts waste more of each course, and decorative or shake work can reach twenty. Use the quick picks or type your own percentage — a valid override always wins over the preset — and the tool nudges you higher when a wall is a gable. ### Which siding profile should I pick? Pick the product you are actually buying: vinyl lap in Double-4, Double-4.5 or Double-5 for the common horizontal look, fiber-cement lap for HardiePlank-style boards, horizontal or vertical panel, board & batten for a vertical batten look, or shakes for cedar-style courses. The profile sets the coverage and exposure defaults and changes the piece count and the diagram coursing; the squares stay the same. ### How do I deduct doors and windows? On a wall in dimensions mode, add each opening with its width, height and count, and its area is subtracted from the gross wall area before the pieces are worked out. The same openings also add their perimeter to the J-channel total. In area mode the number you enter is treated as the finished net area and nothing is deducted. ### Does the calculator work in metric and imperial? Both. Switch units at the top and the geometry converts — walls and gable rise in m or ft, area in m² or ft², exposure and panel width in mm or inches. The headline reads in squares in imperial and square metres in metric. Because coverage rates and stock lengths do not carry across systems, switching units resets the product and accessory settings to that region's defaults. ### Is the calculator private? Yes. Every calculation runs entirely in your browser. Nothing you enter is sent to any server, and your project is saved only in your own browser's local storage. _On the page: https://siteometry.com/en/tools/siding-calculator#faq_ ## Related calculators - [Roofing Calculator — Pitch, Area & Materials](https://siteometry.com/en/tools/roofing) - [Roof Truss Calculator — How Many Trusses & Cost](https://siteometry.com/en/tools/roof-truss-calculator) - [Gutter & Downspout Calculator](https://siteometry.com/en/tools/gutter-downspout-calculator) - [Roof Pitch Calculator — Slope to Degrees, Percent & X-in-12](https://siteometry.com/en/tools/roof-pitch-calculator)