Example 1
- Length: 4 m
- Width: 3 m
Perimeter: 14 m
This kind of result can be used immediately for a first estimate of skirting boards.
Room perimeter calculator
Type length and width. The calculator computes 2×(length plus width), adds a second room, subtracts doors, and adds waste. A 4 by 3 m room is 14 m. A 5.5 by 4.2 m living room is 19.4 m.
A room perimeter calculator is useful for skirting boards, trims, finishing profiles, and any job where total edge length matters. It is also a good starting point for quickly checking other calculations. Also useful: wall area, floor area.
Results
Length room 1 (m), Width room 1 (m), Length room 2 (optional, m) and Width room 2 (optional, m). The result shows up here.
How the results are calculated
Room perimeter counts edge meters for trim, profiles, and casings. For a rectangle P = 2×(length plus width). Two rooms are summed, then door widths come off, then you multiply by (1 plus waste). Price times the result sketches cost when you type it.
A 4 by 3 m bedroom is 14 m, one trim pack around four walls. A 5.5 by 4.2 m living room is 19.4 m. A 6 by 4 m rectangle is exactly 20 m. An 80 cm door between two rooms comes off so you do not buy trim across the threshold.
Type length and width of room 1 in the header unit. A second room, door count, door width in cm, waste, and price are optional. Empty doors deduct nothing. A comma in 5.5 works like 5,5. Door width 80 is centimeters; the calculator converts it to meters.
Floor area 5 by 4 m is 20 m², a different formula. Walls 4 by 3 by 2.6 m are 36.4 m² of paint. Boards for 20 m² at 14 cm are 154.29 linear meters, also not this perimeter.
Ten percent waste on 14 m adds 1.4 m for corners and cuts. Two 4 by 3 m rooms with no door are 28 m; one 80 cm door drops that to 27.2 m before waste. Mixing meters with centimeters in a length field breaks the scale.
Type 4 and 3, click Calculate, and match 14 m. Then 5.5 and 4.2: 19.4 m. Finally 6 and 4: 20 m.
How to use this calculator
- Type length and width of the first room in the header unit, for example 4 and 3.
- Add a second room only when trim runs there too. Both rectangles are summed.
- Subtract doors: count and width in centimeters, for example 1 and 80.
- Add waste for cuts, usually 5-10%, and a price per meter if you want cost.
- Click Calculate. 4 by 3 m is 14 m. 5.5 by 4.2 m is 19.4 m.
Perimeter 2×(length + width)
A 4 by 3 m room is 14 m. A 5.5 by 4.2 m living room is 19.4 m. A 6 by 4 m rectangle is 20 m of trim, not 24 m² of floor.
- perimeter
- Linear metres. 14 m from 4×3. 19.4 m from the living room. An 80 cm door comes off this number.
- m
- Trim unit. 20 m at 6 by 4. That is not 20 m² of floor.
Example scenarios
Example 2
- Length: 5.5 m
- Width: 4.2 m
Perimeter: 19.4 m
In bigger rooms, perimeter quickly shows the scale of finishing work along the edges.
Example 3
- Length: 6 m
- Width: 4 m
Perimeter: 20 m
This is also a convenient value to convert later into wall area once room height is added.
Example 4
- 2.2 × 1.8 m
- 1 door 80 cm
- +8% waste
7.78 m
How many meters of trim for a 2.2×1.8 m bathroom minus an 80 cm door? 7.78 m.
Example 5
- 4 × 3 m
- 1 door 80 cm
- +8% waste
14.26 m
How many meters of trim for a 4×3 m room minus an 80 cm door? 14.26 m.
Example 6
- 5.8 × 4.5 m
- 1 door 90 cm
- +7% waste
21.08 m
How many meters of trim for a 5.8×4.5 m living room minus a 90 cm door? 21.08 m.
Example 7
- 8 × 1.2 m
- 2 doors 80 cm
- +10% waste
18.48 m
How many meters of trim for an 8×1.2 m hallway minus two 80 cm doors? 18.48 m.
Example 8
- 5.5 × 3 m
- 1 door 240 cm
- +5% waste
15.33 m
How many meters of trim for a 5.5×3 m garage minus a 240 cm door? 15.33 m.
Related calculators
FAQ
What perimeter is a 4 by 3 m room?
14 m. 2×(4+3) = 14. That much trim on four walls with no door and no waste.
What perimeter is a 5.5 by 4.2 m living room?
19.4 m. 2×(5.5+4.2) = 19.4. Same formula, the living-room sides.
What perimeter is a 6 by 4 m rectangle?
20 m. Exactly twice the side sum, 2×(6+4). That is trim or skirting, not 24 m² of floor.
How do I subtract an 80 cm door?
Door count 1 and width 80 in centimeters. From 14 m you keep 13.2 m before waste.
What waste should I add for trim?
Usually 5-10% for corners and cuts. 10% on 14 m is an extra 1.4 m.
Is 20 m of perimeter the same as 20 m² of floor?
No. 6 by 4 m is 20 m of perimeter and 24 m² of floor. A 5 by 4 m floor is 20 m² with an 18 m perimeter.
How do I add two 4 by 3 m rooms?
Type the second 4 and 3. Sum 28 m, minus a shared door, then waste.
Where do I count walls for paint?
On wall area: 4×3×2.6 m is 36.4 m². Perimeter stays in linear meters.
Do empty doors deduct zero?
Empty doors deduct nothing. A typed zero also leaves the full perimeter.
How many 2.5 m sticks for 14 m?
Round pieces up: 14 / 2.5 = 5.6, so 6 sticks. The calculator gives meters, not board count.
Knowledge sources
Volume and waste come from the sizes you type. Below are volume and NIST SI units.
Page updated in 2026.