How the baseboard calculator works
Trim is bought by the running metre or foot, so the only measurement that matters is the length of wall at floor level. That is the room perimeter minus every gap where a door casing meets the floor. A margin is then added for mitres, scarf joints and the odd split end, and the total is divided by the stock length.
Pieces = ⌈ (2 × (length + width) − doors × opening width) × (1 + margin) ÷ stock length ⌉Window openings are not deducted because baseboard runs underneath them. Wide archways, fitted kitchen units and built-in wardrobes are, so add them as extra "doors" with their own width.
Worked example
A 5 m × 4 m lounge has an 18 m perimeter. One door opening of 90 cm leaves 17.1 m of skirting. A 10% margin brings the order to 18.81 m, and 18.81 ÷ 2.4 m = 7.8, so you buy 8 lengths. In a 16 × 13 ft room with one 36 in opening the run is 55 ft; with 10% that is 60.5 ft, or four 16 ft pieces, six 12 ft pieces or eight 8 ft pieces. The longer lengths leave fewer joints, but check they fit in your car and up the stairs.
Common trim profiles and sizes
| Profile | Typical height × thickness | Where it is used |
|---|---|---|
| Colonial / ogee (US) | 3-1/4 in × 9/16 in, 5-1/4 in × 5/8 in | Traditional homes |
| Ranch / clamshell (US) | 2-1/4 to 3-1/2 in × 7/16 in | Budget and rental rooms |
| Square-edge MDF | 70–120 mm × 12–18 mm | Modern, painted interiors |
| Torus / ovolo (UK) | 119–169 mm × 15–18 mm | Period properties |
| Solid oak or pine | 70–145 mm × 14–20 mm | Stained or varnished finishes |
| Quarter round / shoe mould | 3/4 in, 12–20 mm | Covers expansion gaps of floating floors |
Cutting and fitting advice
- Cope inside corners. Walls are rarely at exactly 90°. A coped joint (one piece cut square, the other shaped to its profile) stays tight when a plain 45° mitre opens up.
- Mitre outside corners at about 45°, but measure the actual angle with a bevel gauge; a chimney breast can be 92° on one side and 88° on the other.
- Join long walls with a scarf joint, two opposing 45° cuts over a stud, rather than a butt joint that shows a line when the timber shrinks.
- Fix into studs or with adhesive. Nail at every stud, usually 16 in or 400–600 mm apart, two nails per stud for tall boards; on masonry walls use grab adhesive or plugs and screws.
- Acclimatise solid wood in the room for a few days so it does not shrink away from the corners after fitting.
- Buy one spare length of the same profile; mouldings from different production runs can differ by a millimetre and show at a joint.
Frequently asked questions
How much baseboard do I need for a 12×12 room?
The perimeter is 48 ft. Minus one 3 ft door opening that is 45 ft, or 49.5 ft with a 10% margin: five 12 ft, four 16 ft or seven 8 ft pieces.
Do you subtract doors when measuring for baseboard?
Yes. Deduct the full width of each opening including the casing on both sides, typically 34–40 in or 85–100 cm for a standard interior door.
How much extra baseboard should I buy?
Add 10% for a simple rectangular room and 15% for rooms with many outside corners, bay windows or if you are new to coping and mitring.
What lengths does baseboard come in?
In the US, 8, 12 and 16 ft are standard, with some MDF sold in 14 ft. In Europe skirting is usually sold in 2.4 m, 2.5 m or 3 m lengths, and 4.2 m in some UK merchants.
Should baseboard go on before or after flooring?
Fit it after hard flooring so it covers the expansion gap along the walls. With carpet, fit it first and raise it about 10–15 mm (1/2 in) above the subfloor so the carpet tucks underneath.
Last reviewed: 2026-09-27 · How we calculate