How it works
The calculator finds the length of floor edge that needs molding, adds your extra allowance and divides by the length of one piece.
Perimeter = 2 × (Length + Width) or entered directly
Run = Perimeter − Doorways and gaps
Run incl. extra = Run × (1 + Extra ÷ 100)
Pieces = ⌈ Run incl. extra ÷ Piece length ⌉
Length you buy = Pieces × Piece length
⌈ ⌉ means rounding up to the next whole piece. Rounding happens only at the end.
Why quarter round goes in after a floating floor
A floating floor – laminate, most click vinyl plank and floating engineered wood – isn’t fastened to the subfloor. It expands and contracts with temperature and humidity, so it is laid with a gap at every wall. Pergo’s laminate installation guide is a typical example: it says expansion gaps are mandatory on the entire perimeter of the floor, and that “a floating installation should remain floating”. The gap it gives for floating floors is 1 mm per meter of floor width, with a minimum of 8 mm.
That gap has to be hidden. If the old baseboard comes off before the floor goes down, it can be reinstalled over the gap. Many people leave the baseboard on the wall instead and add quarter round or shoe molding along its foot. Quick-Step, for example, says its scotia “can also come in handy as a finish in combination with existing skirtings”. This calculator counts the pieces for that finishing step.
How to measure the run
For a rectangular room, enter its length and width; the calculator doubles their sum to get the perimeter. For anything else – an L-shaped room, a hall with several doors, an open plan – measure each length of wall where the molding will go, add them up and enter that as the perimeter.
Then work out where the molding stops. Door openings are the obvious ones: the molding ends at the door casing. Also subtract the width of transition strips at the edge of another floor, hearths, stair nosings and kitchen cabinets. Enter the total of all those stops under doorways and gaps. A closet without a door that gets new flooring inside is not a gap – the molding usually continues into it, so add its walls to the perimeter instead.
Picking a piece length
Quarter round is sold in fixed lengths that vary by maker and store. Alexandria Moulding, for example, lists 3/4 × 3/4 in quarter round in 8 ft lengths, with 12 ft pro packs and random lengths in the same profile; Quick-Step lists its scotia at 2400 mm long. The 8 ft and 2.4 m values in the form are only examples – enter the length you’ll actually buy.
Longer pieces mean fewer joints on long walls, but they are harder to carry and cut, and short walls waste more of each piece. If the room has many short walls, compare the total length with the walls one by one: a 5 ft wall cut from an 8 ft piece leaves a 3 ft offcut that is useful only if another wall is 3 ft or shorter.
Corners and the extra allowance
Each inside corner is usually coped or mitered, and each outside corner is mitered, so the ends of every piece use some length. A bad cut means recutting. The extra allowance adds a percentage to the run before the pieces are counted. It starts at 0 % so you see the minimum; increase it for rooms with many corners. Rounding up to whole pieces already leaves some spare – in the example, 51 ft of run needs 7 pieces of 8 ft, which is 56 ft, or 5 ft to spare.
Size of the molding
Before you buy, check the molding against the gap. The molding has to cover the gap with the floor still free to move under it. Quick-Step’s scotia, for example, measures 17 × 17 mm, and Alexandria’s quarter round in the example is 3/4 × 3/4 in. If your flooring’s instructions call for a larger gap – some do for long rooms or humid conditions – make sure the molding is wider than the gap you actually left.
Fastening
How trim is attached is part of your flooring’s instructions, and they come first. Pergo’s guide says to attach the skirtings to the wall, never to the floor, so the floor can keep moving under them. Quick-Step says its scotia is easy to install with its One4All glue; other trim makers give their own methods. Whatever you use, the molding must not pin the floor down – Pergo’s guide also says a floating floor must never be fixed or blocked.
Worked example
Inputs
- Measure by
- Room length × width
- Room length
- 15 ft
- Room width
- 12 ft
- Doorways and gaps
- 3 ft
- Piece length
- 8 ft
- Extra allowance
- 0 %
Result
- Room perimeter
- 54 ft
- Quarter round run
- 51 ft
- Run incl. extra
- 51 ft
- Pieces
- 7
- Length you buy
- 56 ft
Common mistakes
- Subtracting doorways but forgetting other stops – transition strips, fireplace hearths, stair nosings and cabinets that already hide the floor edge.
- Counting only total length. A room with several short walls produces offcuts that are too short to reuse, so it can need more pieces than the run suggests.
- Fastening the molding down into a floating floor. The floor has to stay free to move under the trim; follow your flooring’s instructions for how trim is attached.
- Buying molding narrower than the gap. A gap that shows past the edge of the molding defeats the purpose – compare the molding size with the expansion gap you left.
- Mixing piece lengths when comparing prices. A price per piece only compares fairly between products of the same length – compare per linear foot or meter.
Assumptions and limits
- In room mode, the room is a rectangle; the perimeter is 2 × (length + width). For other shapes, enter the perimeter.
- Doorways and gaps are subtracted as one total length.
- Pieces are counted from total length and rounded up to whole pieces. Individual cuts, corners and joints are not planned.
- Molding is needed along every wall included in the perimeter; baseboard, nails, glue, caulk and paint are not included.
Frequently asked questions
What is the difference between quarter round and shoe molding?
Both are small moldings that sit where the baseboard meets the floor. Quarter round has a profile of a quarter circle; shoe molding is usually a little taller than it is deep. For counting pieces the difference doesn’t matter – the run and the piece length are what count.
Do I need quarter round with a floating floor?
You need something that hides the expansion gap at the walls. Pergo’s laminate guide, for example, says expansion gaps are mandatory on the entire perimeter of the floor. If you take the baseboard off and reinstall it, it may cover the gap by itself; if you leave the baseboard in place, quarter round or shoe molding is the usual way to cover it.
How wide is the expansion gap I need to cover?
It is set by your flooring’s installation instructions. Pergo’s 07.2026 laminate guide, for example, gives 1 mm per meter of floor width with a minimum of 8 mm for floating floors up to 13 × 13 m. Check that your molding is wider than that gap.
How much extra should I buy?
It depends on the number of corners and on how well the offcuts fit the shorter walls. The calculator starts at 0 % extra; the safest check is to list the walls and fit them against the piece length you can buy. Rounding up to whole pieces already leaves some spare length.
Can I use this for baseboard?
The arithmetic is the same, but baseboard often stops at different places, for example cabinets where quarter round may still run along the toe kick. The baseboard calculator has its own page and help text for that task.
Sources
- 0W105 Quarter Round – product page — Alexandria Moulding. Quarter round sold in 8 ft pieces: "Oak Quarter Round 3/4 x 3/4 x 8'" (also 12 ft pro packs and random lengths); US default uses 8 ft.
- Quick-Step Scotia (QSSCOT04761) – product page — Quick-Step (Unilin). Scotia for floors: "Height 17 mm Length 2400 mm Width 17 mm" (metric default uses 2.4 m); "A scotia can also come in handy as a finish in combination with existing skirtings. It is easy to install with One4All Glue."
- Installation Guide – Laminate Flooring (version 07.2026) — Pergo (Unilin). Floating floors: "Expansion gaps are mandatory on the entire perimeter of the floor"; gap "1 mm/m floor width with a minimum of 8mm"; "A floating installation should remain floating!"; "Attach the skirtings to the wall (never to the floor)."
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 3, 2026