What is a siding square?

One square is 100 square feet (9.2903 m²) of wall coverage.

How much waste should I add?

10% is common for simple elevations. Increase to 12–15% for complex facades, diagonal installations, or many small cuts.

How do I calculate a gable wall?

Add the rectangle area (width × wall height) and the triangle area (0.5 × width × gable peak height).

What does box coverage mean?

Many vinyl siding boxes cover roughly 2 squares (200 sq ft), but always check the manufacturer’s stated net coverage per box.

How are accessory pieces estimated?

Starter strips are based on total base length; J-channel on opening perimeters; corner trims on the number of corners times wall height, divided by the piece length.

Can I switch between feet and meters?

Yes. Toggle the unit system to enter dimensions in ft/in or metric. Results adapt automatically.

Siding Calculator

Use this professional siding calculator to estimate net wall area, apply a realistic waste allowance, and convert the result into siding squares, boxes, individual panels, and accessory pieces. It’s designed for contractors, estimators, and DIYers who need accurate quantities fast.

Inputs

Feet (ft) Meters (m)

Switch units at any time—values update automatically.

Typical eave wall height *

Waste allowance (%) *

Box coverage (area per box) *

ft²

Effective coverage per panel

ft²

Number of outside corners

Accessory piece length

Cost basis

Cost amount

Walls

Openings (windows/doors)

Results

Gross wall area 0.00 ft²

Openings area 0.00 ft²

Net wall area 0.00 ft²

Total with waste 0.00 ft²

Squares needed

0.00

Rounded up: 0

Boxes needed

0.00

Rounded up: 0

Panels needed

—

Rounded up: —

Estimated cost

—

Accessories

Starter strip length 0.00 ft

Starter strip pieces 0

J-channel length (around openings) 0.00 ft

J-channel pieces 0

Corner trim pieces 0

Note: Quantities are rounded up to whole pieces for ordering. Results are provided for planning and estimation; verify against manufacturer specs and plans.

Data Source and Methodology

Primary source: Vinyl Siding Institute (VSI), “Vinyl Siding Installation Manual, 11th Edition,” 2020. Direct link: VSI Installation Manual PDF.

Supporting reference for standard geometric area formulas: NIST, “Handbook of Mathematical Functions,” 2010.

Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.

The Formula Explained

Gross\ Area:\quad A_{\text{walls}} = \sum \left( w \times h \right) + \sum \left( w_g \times h_g^{\text{wall}} + \tfrac{1}{2} w_g \times h_g^{\text{peak}} \right)

Openings\ Area:\quad A_{\text{open}} = \sum \left( w_i \times h_i \right) Net\ Area:\quad A_{\text{net}} = A_{\text{walls}} - A_{\text{open}} Waste\ Applied:\quad A_{\text{tot}} = A_{\text{net}} \times \left(1 + \frac{p_{\text{waste}}}{100}\right) Squares:\quad \text{Squares} = \frac{A_{\text{tot}}}{100\ \text{ft}^2} Boxes:\quad \text{Boxes} = \frac{A_{\text{tot}}}{C_{\text{box}}} Panels:\quad \text{Panels} = \frac{A_{\text{tot}}}{C_{\text{panel}}}

Starter\ Pieces:\quad N_{\text{starter}} = \left\lceil \frac{L_{\text{base}}}{L_{\text{piece}}} \right\rceil,\quad J\text{-channel Pieces}: \left\lceil \frac{L_{\text{openings}}}{L_{\text{piece}}} \right\rceil

Corner\ Pieces:\quad N_{\text{corner}} = N_{\text{corners}} \times \left\lceil \frac{H_{\text{typ}}}{L_{\text{piece}}} \right\rceil

Glossary of Variables

w, h: wall width and height.
w_g: gable wall width; h_g^wall: wall height below eave; h_g^peak: additional triangular peak height.
A_walls: total wall area before subtracting openings.
A_open: total area of all windows and doors.
A_net: A_walls − A_open.
p_waste: waste percentage; A_tot: net area with waste applied.
Squares: A_tot divided by 100 ft².
C_box: net coverage per box (area).
C_panel: effective coverage per panel (area).
L_base: sum of wall base widths (starter strip run).
L_openings: sum of perimeters of all openings.
L_piece: length of a single accessory piece (e.g., 10 ft).
N_corners: number of outside corners; H_typ: typical wall height for corner trims.

Come Funziona: Un Esempio Passo-Passo

Inputs: Two rectangular walls (20 ft × 9 ft and 15 ft × 9 ft), one gable wall (24 ft width, wall height 8 ft, peak height 4 ft). Openings: two windows (3 ft × 4 ft), one door (3 ft × 6.8 ft). Waste 10%. Box coverage 200 ft². Panel coverage 8.3 ft². Piece length 10 ft. Outside corners: 4. Typical height 9 ft.

Compute wall areas: A_rect1 = 20×9 = 180 ft²; A_rect2 = 15×9 = 135 ft²; A_gable = 24×8 + 0.5×24×4 = 192 + 48 = 240 ft². Gross A_walls = 180 + 135 + 240 = 555 ft².

Openings: 2×(3×4) + (3×6.8) = 24 + 20.4 = 44.4 ft². Net A_net = 555 − 44.4 = 510.6 ft².

With waste: A_tot = 510.6 × (1 + 0.10) = 561.66 ft². Squares = 561.66 / 100 = 5.62 → round up to 6 squares. Boxes = 561.66 / 200 = 2.81 → round up to 3 boxes. Panels = 561.66 / 8.3 = 67.67 → round up to 68 panels.

Accessories: L_base = 20 + 15 + 24 = 59 ft → starter pieces = ceil(59/10) = 6. J-channel around openings: perimeter = 2×[(3+4) + (3+6.8)] = 2×(7 + 9.8) = 33.6 ft → pieces = ceil(33.6/10) = 4. Corner trims: 4 × ceil(9/10) = 4.

Frequently Asked Questions (FAQ)

What’s the difference between gross, net, and total with waste?

Gross is all wall area before subtracting openings. Net subtracts windows and doors. Total with waste adds a percentage to cover cuts and off-cuts that aren’t reusable.

Is 200 ft² per box always correct?

No. Coverage varies by profile and brand. This tool lets you set the exact coverage per box—use your product’s datasheet.

How accurate is the panel count?

Panel counts depend on the net exposed coverage per panel. Enter the manufacturer’s effective coverage for the most accurate result.

Should I include sheathing wrap or nails in this estimate?

This calculator focuses on cladding and select accessories. Add fasteners, house wrap, flashing, and sealants per code and manufacturer requirements.

Can I use this for fiber-cement or wood siding?

Yes—the area math is the same. Adjust box/panel coverage and waste to match the specific product and installation pattern.

How do I handle complex elevations?

Break them into smaller walls (add more wall entries) and include special areas separately. Increase waste for heavy detailing.

Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Team.
Last reviewed for accuracy on: September 15, 2025.