Baseboard Length Calculator

Baseboards (also called skirting boards in the UK and Australia) are the trim pieces that run along the bottom of interior walls where they meet the floor. They protect the wall from scuffs and furniture, cover the gap between the wall and floor, and add a finished look to any room.

Calculating baseboard length: The basic formula is the perimeter of the room minus the width of all doorways. But there are several additional factors to account for:

Step 1: Measure the room perimeter Measure all four walls and add them together. For non-rectangular rooms, break it into sections and add all wall lengths.

Step 2: Subtract door openings For each doorway, subtract the door frame width from the perimeter. Standard interior door openings are about 900mm / 36 inches (frame to frame). You’ll still need baseboard on the sides of the doorway, but not across the opening itself.

Step 3: Add waste factor Always order more than your calculated length. Baseboard is mitered at corners (45° cuts), and each miter joint wastes a small amount. Additionally, boards come in fixed lengths (usually 240cm / 8ft, 360cm / 12ft, or 480cm / 16ft in most markets), so you’ll have offcuts.

Standard waste allowance:

• Simple rectangle room: add 10%
• Room with many corners, angles or a fireplace surround: add 15%

Pick the matching option in the calculator. The 15% figure is not padding for its own sake. Every extra inside corner means another coped end, and coping is the one cut a beginner ruins repeatedly.

Step 4: Calculate board count Divide total length needed by the board length you’re buying, then round up.

Rounding up is where people get caught out. Ten boards at 2.4 m is 24 m of material, but if your longest wall is 4.5 m you cannot make that wall from a single 2.4 m board, so you need a scarf joint or a longer board. Buy the longest board that fits in your car and your hallway.

Metric vs Imperial: This calculator works in both meters and feet. Pick the unit at the top and enter every measurement in that unit. The board lengths follow your choice too: choose feet and you get true 8, 10, 12 and 16 foot boards, not their metric near-equivalents.

Worked example: A 4.5 m by 3.5 m rectangular bedroom with one 0.9 m doorway.

Perimeter = 4.5 + 3.5 + 4.5 + 3.5 = 16.0 m Less the doorway = 16.0 − 0.9 = 15.1 m net With 10% waste = 15.1 × 1.10 = 16.61 m At 2.4 m boards = 16.61 ÷ 2.4 = 6.92, so buy 7 boards (16.8 m purchased)

That leaves 1.7 m of offcut over the net length, which sounds generous until you remember that every offcut shorter than about 300 mm is scrap.

Tips for installation:

• Inside corners: one piece runs to the corner, the second piece is coped (not mitered) for a better fit
• Outside corners: both pieces mitered at 45°
• Seal all gaps with paintable caulk after installation
• Pre-prime and paint baseboard before installing for easier touch-up later