Example 1
- Length: 4 m
- Width: 3 m
Perimeter: 14 m
How many meters of trim for a 4×3 m room? 2×(4+3) → 14 m.
Room Perimeter Calculator
Enter length and width in the header unit. The calculator computes 2×(length + width), adds a second room, subtracts doors, and adds waste. A 4×3 m room is 14 m. A 5.5×4.2 m living room is 19.4 m. With an 80 cm door and 8% you get 14.26 m.
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.
Linear-meter estimate for trim and casing around a rectangular room. Get area from floor area. Related: wall area.
How the results are calculated
L4 m
W3 m
P14 m
The perimeter calculator counts linear meters of edges for trim, profiles, and casings. The formula is max(0, sum of 2×(length + width) − doors) × (1 + waste/100). Door width is entered in centimeters; the calculator converts it to meters.
A 4×3 m room is 14 m. A 5.5×4.2 m living room is 19.4 m. A 6×4 m rectangle is 20 m. With one 80 cm opening and 8% waste on 4×3 m the result is 14.26 m.
Enter length and width of the first room in the header unit. A second room, doors, waste, and price are optional. Empty doors deduct nothing. A comma in 5.5 works the same as a period.
Floor area 5×4 m is 20 m² — a different formula. Walls 4×3×2.6 m are 36.4 m² of paint. Boards for 20 m² at 14 cm are 154.29 linear m, not this perimeter.
Ten percent waste on 14 m adds 1.4 m for corners. Two 4×3 m rooms with no doors are 28 m; one 80 cm door leaves 27.2 m before waste. Keep meters in the length field, not centimeters.
Enter 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
- Enter 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 (or inches in US units), for example 1 and 80.
- Add waste for cuts, usually 5–10%, and a price per meter if you want cost.
- Click Calculate. 4×3 m is 14 m. With an 80 cm door and 8% you get 14.26 m.
Formula
P = max(0, Σ 2×(L + W) − doors) × (1 + waste/100)
A 4×3 m room: 2×(4+3) = 14 m. Minus a 0.80 m door and plus 8%: 13.2 × 1.08 = 14.26 m.
Perimeter and doors
Sides summed twice, doors subtracted, waste added. A 4×3 m room is 14 m. With an 80 cm opening and 8% you get 14.26 m.
- P
- Perimeter in linear meters. 2×(4+3) = 14. A 5.5×4.2 m living room is 19.4 m.
- doors
- Width in cm. 80 cm = 0.80 m deducted. From 14 m you keep 13.2 m before waste.
- waste
- Cutting percent. 8% on 13.2 m is 14.26 m. 10% on 14 m adds 1.4 m.
- m²
- Floor area on another page. 6×4 m is 24 m² and 20 m perimeter here.
Example scenarios
Example 2
- Length: 5.5 m
- Width: 4.2 m
Perimeter: 19.4 m
A 5.5×4.2 m living room → 19.4 m.
Example 3
- Length: 6 m
- Width: 4 m
Perimeter: 20 m
A 6×4 m rectangle → 20 m of trim (not 24 m² of floor).
Example 4
- 2.2 × 1.8 m
- 1 door 80 cm
- +8% waste
7.78 m
max(0, 8 − 0.80) × 1.08 = 7.78 m.
Example 5
- 4 × 3 m
- 1 door 80 cm
- +8% waste
14.26 m
4×3 m with an 80 cm door and 8% waste → 14.26 m.
Example 6
- 5.8 × 4.5 m
- 1 door 90 cm
- +7% waste
21.08 m
max(0, 20.6 − 0.90) × 1.07 = 21.08 m.
Example 7
- 8 × 1.2 m
- 2 doors 80 cm
- +10% waste
18.48 m
max(0, 18.4 − 1.60) × 1.10 = 18.48 m.
Example 8
- 5.5 × 3 m
- 1 door 240 cm
- +5% waste
15.33 m
max(0, 17 − 2.40) × 1.05 = 15.33 m.
Related calculators
Frequently asked questions
How do I calculate room perimeter from length and width?
Add length and width, then multiply by 2. A 4×3 m room → 2×(4+3) = 14 m. Optionally subtract doors and add waste.
How many meters of trim for a 4×3 m room?
14 m with no doors and no waste. With one 80 cm opening and 8% waste the result is 14.26 m. A 5.5×4.2 m living room is 19.4 m.
How does perimeter differ from floor area or board linear meters?
Perimeter is edge length: 2×(L+W). Floor area 5×4 m is 20 m². Boards from area and width live on a sibling card, not this result.
Does the result replace a baseboard or trim plan?
No. It is a length estimate. Cuts, joints, and stock stick lengths still need a separate decision.
Is this a free room perimeter calculator?
Yes. Enter length and width, optional doors and waste, and you see meters at once. No account required.
How is room perimeter calculated?
The calculator sums 2×(length + width) for each rectangle, subtracts door width, and multiplies by (1 + waste/100). A 4×3 m room with no doors is 14 m. With one 80 cm opening and 8% waste you get 14.26 m.
Which unit should I use for the sides?
The header unit, usually meters. Four hundred centimeters is 4, not 400. Entering 400 would overstate the side a hundred times.
How do I subtract doors?
Enter door count and width in centimeters (or inches in US units), for example 1 and 80. From 14 m you keep 13.2 m before waste. Empty fields deduct nothing.
What waste should I add for trim?
Usually 5–10% for corners and cuts. On 14 m net, 10% waste adds 1.4 m. On 13.2 m after doors, 8% yields 14.26 m.
How does perimeter differ from floor area?
Here you count linear meters of edges. A 6×4 m floor is 24 m² on the floor-area page, while the same rectangle’s perimeter is 20 m.
Why enter a second room?
To sum two rectangles before doors and waste. Two 4×3 m rooms are 28 m. One 80 cm door between them leaves 27.2 m before waste.
Does a comma in 5.5 work?
Yes. A comma and a period are the same length. At 5.5×4.2 m the result stays 19.4 m.
What is the primary result?
Perimeter in linear meters, for example 14 m. Cost appears beside it when you fill a price per meter.
Where do I calculate walls or boards?
Walls on the wall-area page: 4×3×2.6 m is 36.4 m². Boards take m² from floor area, not this perimeter.
Does the result replace a trim plan?
No. The calculator is a purchase estimate for rectangles with optional doors. An irregular shape should be split into simpler figures.
Knowledge sources
Rectangle perimeter is 2×(length + width). Units below from NIST.
Page updated October 29, 2026.