Estimate interior door replacements from opening and casing measurements
An interior-door replacement budget depends on more than the number of slabs or prehung units being ordered. A project may also require casing trim, new hinges, latchsets, wall repairs and removal of the old doors. The calculator counts door units directly, derives casing footage from nominal opening measurements and prices the selected hardware separately. It keeps installation and removal labor as individual user-entered amounts so quoted work is not silently folded into a flat material price.
For each finished side of a door opening, the basic casing takeoff uses two vertical legs and one horizontal header. Multiplying by the selected number of visible casing sides and door openings produces nominal linear footage. A cutting allowance is added before dividing by the purchased trim-stick length, and the result is rounded up to whole stock pieces. This is a preliminary linear-foot allowance, not an exact cut optimization for mitered joints and product-specific stock sizes.
Door trim and hardware formulas
Trim sticks = round up (nominal casing × (1 + waste % ÷ 100) ÷ stock-stick length)
Hinges = door count × hinges per door
Latchsets = door count
Project budget = quoted doors + casing + hardware + labor + removal + other work
Worked example: replacing five interior doors
Five interior openings, each approximately 6.67 feet high and 2.67 feet wide, need about 80.1 feet of casing per finished side of the collection of doors. If both faces are trimmed, the combined length is about 160.1 feet. With a ten-percent allowance, the purchase requirement is roughly 176.1 feet. Eight-foot sticks require 23 whole pieces.
At three hinges per door, the replacement also calls for fifteen hinges and five handle sets. Those counts are multiplied by the visitor's material quotes; installation and removal costs remain separate from the hardware totals.
Confirm what is included in each door quote
Slab-only and prehung interior doors are different products. A slab may require accurate mortising and fitting into an existing jamb, while a prehung unit includes a jamb assembly and can involve more trim disturbance. Fire-rated doors, doors at garage separations and other protected openings have special requirements that should not be treated as ordinary interior partitions. Verify handing, swing clearance, wall thickness, frame condition and finished floor height before ordering.
Replacement quotes may include disposal, painting, stops, hinges and casing—or omit nearly all of them. The optional additional-work field is for scope items supported by a quote, such as wall patching or threshold changes. Measuring every opening is important in older homes where nominally identical doorways can vary.
Interior door installation questions
Does the calculation assume every door has casing on both sides?
No. Choose one or two finished sides according to the actual doorway. The formula multiplies the measured casing outline only by the selected sides and the number of door openings.
Should hinges be priced separately for prehung doors?
Only when they are not included in the purchased unit. Some prehung doors come with installed hinges and the additional hardware cost would be zero. Review the product listing and enter rates accordingly to avoid double-counting.
Will this determine the correct door size?
No. The height and width fields are trim allowances, not a complete rough-opening schedule. Door leaf dimensions, jamb width, clearance and swing must be verified against the actual opening and the selected product.