Baseboard & Trim Calculator
Enter the room's perimeter and its doors and windows. You'll get linear feet and stock pieces for baseboard, door and window casing, and crown molding.
- Tested formulas
- Feet or metric
- Printable shopping list
2 What to buy
Updates as you type| Baseboard | 46.9 ft → 3 16 ft pieces (42.7 ft before extra) |
|---|---|
| Door casing | 36.9 ft → 3 16 ft pieces (33.5 ft before extra) |
| Window casing | 34.1 ft → 3 16 ft pieces (31 ft before extra) |
Piece counts are total length ÷ piece length, so some walls will need a joint. Buy pieces at least as long as your longest wall where you can, and make any joint mid-wall a scarf (two 45° cuts overlapping) so it doesn't open up.
Shopping list
Quick answer
Baseboard = room perimeter − door openings + 10–15%. A 12 × 12 ft room with two 32" doors needs 42.7 ft of baseboard, or 46.9 ft with 10% extra: 3 pieces 16 ft long.
Baseboard for common room sizes
| Room | Linear feet | 8 ft pieces | 12 ft pieces | 16 ft pieces |
|---|---|---|---|---|
| 10 × 10 ft | 41.1 | 6 | 4 | 3 |
| 10 × 12 ft | 45.5 | 6 | 4 | 3 |
| 12 × 12 ft | 49.9 | 7 | 5 | 4 |
| 12 × 14 ft | 54.3 | 7 | 5 | 4 |
| 14 × 16 ft | 63.1 | 8 | 6 | 4 |
| 16 × 20 ft | 76.3 | 10 | 7 | 5 |
One 32" door per room, 10% extra. Use the calculator above for your exact size.
How to measure for trim
For baseboard, add up the length of every wall and take off the door openings, then add 10 to 15% for miters and offcuts, as Home Depot's moulding guide recommends. Crown molding runs the full perimeter with no gaps for doors.
Door casing takes two legs and a head on each side of the door. Home Depot's formula is 2 × the door height + the width + 4 × the casing width, which allows for the miters at the top corners. Window casing is the window's perimeter plus 8 × the casing width.
Worked example: a 12 × 12 ft bedroom
- Perimeter: 48 ft, less two 32" doors = 42.7 ft of baseboard. With 10% extra: 46.9 ft, or 3 pieces at 16 ft.
- Door casing, one side: 2 × 80 + 32 + 4 × 2¼ = 201" per door, 33.5 ft for two. With 10%: 3 pieces.
- Window casing: 2 × (36 + 48) + 8 × 2¼ = 186" per window, 31 ft for two: 3 pieces.
Tips for fewer joints and less waste
- Buy pieces long enough to run each wall in one length where you can. Joints show, especially on painted trim.
- Where you must join two pieces on a long wall, use a scarf joint (two 45° cuts) over a stud.
- Nail into the studs every 16 to 18 inches with 1½ to 2 inch finish or brad nails.
- Let wood trim sit in the room for a couple of days before cutting so it adjusts to the humidity.
Frequently asked questions
How do I calculate how much baseboard I need?
Measure every wall, add them up, and subtract the width of each doorway. Add 10 to 15% for miters and offcuts, then divide by the length of the pieces you're buying and round up.
How much door casing do I need per door?
For one side of a standard 36 × 80 inch door with 2¼ inch casing, about 205 inches (17 ft) before waste, using Home Depot's formula of 2 × height + width + 4 × casing width.
What lengths does baseboard come in?
Common lengths are 8, 12 and 16 ft, and some casing comes in 17 ft lengths. Longer pieces mean fewer joints.
How much extra trim should I buy?
10 to 15% more than the measured length covers miter cuts and the occasional bad end.
Last reviewed 2026-10-23. See how we calculate for our sources and assumptions.