Plan a window replacement project by unit and opening
Replacement windows are typically purchased as discrete manufactured units. A home's six windows may have similar-looking frames but different rough-opening measurements and glazing specifications. This calculator applies one set of dimensions and one per-unit quotation to a group of identical openings. For a home with several window sizes, calculate each size group independently and combine the line items from those estimates.
Enter the measured opening width and height in inches to calculate total opening area. That figure can help check how large the project is, but it is not a substitute for the dimensions needed to order replacement units. A rough opening, existing frame, sash and replacement insert may all have different measurement conventions. Confirm which dimension the manufacturer or installer requests before committing to an order.
Opening measurements and line-item pricing
Combined perimeter (linear ft) = window count × 2 × (width + height) ÷ 12
Unit budget = count × window unit price
Installation budget = count × labor price per opening
Trim allowance = combined perimeter × trim rate per linear ft
The trim line is relevant only when casing, exterior trim or interior finishing is priced by measured length. If a contractor includes trim in the per-opening installation price, keep its separate rate at zero. Similarly, enter removal cost only if disposal and tear-out are excluded from the installer quotation. The total applies contingency to the entered subtotal, not to opening area or unit quantity.
Worked example: six matching openings
Suppose six windows each occupy an opening 36 inches wide and 48 inches high. Each opening measures 12 square feet, giving a combined 72 square feet. The perimeter of one opening is 2 × (36 + 48) ÷ 12 = 14 linear feet, so six openings have a combined perimeter of 84 linear feet.
At hypothetical entered quotes of $400 per window, $180 labor per opening, $45 removal per opening and $8 per linear foot of separately priced trim, the subtotal is $2,400 + $1,080 + $270 + $672 = $4,422 before additional work or contingency. These figures show the arithmetic, not current national prices.
What changes the final replacement scope?
Insert replacements that reuse sound existing frames can involve different work from full-frame replacements requiring the surrounding trim, flashing and water-resistive assembly to be rebuilt. Materials, opening size, glass package, operability, energy-performance requirements and second-story access also affect the price. The calculation cannot determine whether concealed wood decay, improper sill drainage or structural modifications are present. Those issues should be evaluated in the installation scope rather than hidden inside a generalized price per window.
For cost comparisons, request that installers identify the window product, installation method, exterior water management, interior finish, disposal and warranty. A lower unit price is not necessarily a lower completed-project cost if required flashing or finishing is excluded.
Window replacement questions
Can I enter windows of different sizes together?
The budget can count any identical price per unit, but its opening-area and trim-perimeter results assume every opening has the same dimensions. Measure and price different size or product groups separately, then add their totals for a project-wide comparison.
Is rough-opening area the same as glass area?
No. The overall opening includes frame space and installation clearances, while visible glass is smaller. Glass area also varies with frame profiles and divider layouts. Use the manufacturer's dimensions for ordering, not the square-foot figure as a glazing specification.
Does the calculation include water damage around windows?
Only if you enter a quoted amount in other costs. Frame rot, wet insulation, siding repair or sill rebuilding may not be evident until trim is removed. The window count and perimeter do not predict concealed damage.