Calculate window valance width, drop, inside or outside mount sizing, board-mounted valance returns, fullness, and fabric yardage before ordering or sewing.
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A valance can look simple, but the finished size depends on the window opening, trim, mount type, rod or board projection, side returns, desired drop, fabric width, pattern repeat, fullness, hems, and waste allowance. This calculator turns those measurements into a conservative planning estimate so a homeowner, renter, decorator, seamstress, or installer can discuss a more precise order without starting from a blank page.
The tool is designed for common residential window treatments: flat tailored valances, gathered rod-pocket valances, and board-mounted valances. It is useful when comparing ready-made sizes, estimating custom workroom yardage, planning a kitchen valance above a sink, checking whether an inside mount has enough depth, or deciding whether an outside mount should cover trim and shade hardware.
For an outside mount, the starting face width is window width + two side overlaps. For an inside mount, the starting width is opening width - inside deduction. If a board or rod projects from the wall, the estimate adds two return depths so fabric can wrap back to the wall. A flat valance uses roughly the finished face width plus returns and hems; a gathered valance multiplies the face width by the fullness setting before adding returns and hems.
The cut drop starts with the desired finished drop plus top and bottom allowances. Board-mounted treatments may need extra allowance for projection or wrapping. The fabric-width count is calculated by dividing total cut width by usable fabric width and rounding up. If a vertical pattern repeat is entered, the tool rounds each cut length up to the next repeat interval, then applies the waste percentage. Yardage is the adjusted total inches divided by 36.
A flat valance usually matches the finished board, rod, or opening face width. Outside mounts commonly add 2 to 4 inches per side to cover trim or shade hardware, plus return depth if the treatment projects from the wall.
Many gathered or rod-pocket valances use about 1.5x to 2.5x fullness. Lightweight sheer fabric may need more fullness; stiff lined fabric may look bulky at the high end.
A common visual range is about 18% to 28% of the window height, but privacy goals, ceiling height, cabinet clearance, shade coverage, and room style can justify a shorter or longer drop.
No. Workrooms may change yardage for seams, lining, railroaded fabric, pleats, trims, contrast bands, motif placement, and manufacturer instructions.
Use the result as a planning range. Before purchasing, confirm fabric width, repeat, direction, roll availability, dye lot, shrinkage, lining, and whether extra fabric is needed for mistakes or future repairs.
This is a general measurement aid, not professional design, sewing, installation, fire-safety, child-safety, or building-code advice. Verify final dimensions with the installer, workroom, hardware instructions, landlord rules, and local requirements. Keep cords, chains, and loose fabric away from children and heat sources. Confirm that anchors, brackets, and boards are suitable for the wall material and treatment weight before installation.