Perimeter Calculator
Calculate perimeter for rooms, yards, and garden beds. Get linear footage for fencing, baseboard, crown molding, and edging — with waste factors and shape formulas for all standard shapes.
Enter your values above to see the results.
Tips & Notes
- ✓For baseboard molding, measure room perimeter then subtract all doorway widths — a standard interior doorway is 32–36 inches, and forgetting even one door opening over-orders a significant length of trim.
- ✓Order crown molding in 16-foot lengths rather than 8-foot to minimize joints — fewer joints mean cleaner corners and less waste from the extra cuts at joints. Longer pieces are harder to handle but produce a professional result.
- ✓For irregular curved boundaries (garden beds, natural stone edges), use a measuring wheel or lay a flexible tape measure along the curve — a straight tape stretched between two points on a curve underestimates its length.
- ✓When calculating fence perimeter, remember that corners share posts — a rectangular fence with 4 corners needs only 4 corner posts, not 8. The perimeter determines rail and picket quantity; post count requires a separate calculation.
- ✓For room baseboard in rooms with inside corners, add 2 inches per inside corner for overlap material needed at mitered joints — the miter cut on each piece extends slightly beyond the nominal room measurement.
Common Mistakes
- ✗Confusing perimeter and area — baseboard is a perimeter (linear) measurement; flooring is an area measurement. Using area calculations for trim material or perimeter for flooring produces wildly incorrect quantities.
- ✗Not subtracting door openings from baseboard perimeter — each standard doorway removes 32–36 inches of baseboard. A room with 3 doors needs approximately 8–9 feet less baseboard than the raw perimeter suggests.
- ✗Measuring along walls at ceiling height for crown molding — room dimensions at ceiling level are not always the same as at floor level. Measure along the actual wall-ceiling junction for crown molding.
- ✗Forgetting outside corners in perimeter calculations for edging — a garden bed with 4 outside corners requires slightly more edging than the calculated perimeter because the edging must curve around each corner.
- ✗Ordering baseboard in lengths that do not match your longest wall — if your longest wall is 15 feet, ordering only 8-foot lengths forces an extra joint. Identify your longest walls before selecting lumber lengths.
Perimeter Calculator Overview
Perimeter is the total distance around the boundary of a shape — the measurement used for fencing, edging, trim, molding, wallpaper borders, and any application where the quantity of material depends on length rather than area. Confusing perimeter with area is one of the most common measurement errors in home improvement projects, leading to either severe material shortfalls or significant overordering.
Perimeter formulas for common shapes:
Rectangle: P = 2 × (Length + Width) | Circle (circumference): P = 2 × π × radius | Triangle: P = a + b + c
EX: Rectangular yard 80 ft × 120 ft → Perimeter = 2 × (80 + 120) = 400 linear feet of fencing neededPerimeter formulas for all standard shapes:
| Shape | Formula | Variables | Common Application |
|---|---|---|---|
| Rectangle | P = 2(L + W) | Length, Width | Fencing, room baseboard |
| Square | P = 4s | Side length | Garden beds, tiles |
| Triangle | P = a + b + c | Three side lengths | Gable trim, corner edging |
| Circle (circumference) | P = 2πr = πd | Radius or diameter | Circular bed edging, pools |
| Regular hexagon | P = 6s | Side length | Paving patterns |
| Irregular polygon | P = sum of all sides | Measure each side | Property fencing, gardens |
| Application | Unit | Waste Factor | Example: 200 LF Perimeter |
|---|---|---|---|
| Fencing | Linear feet | +5% (end posts, gates) | 210 LF fence material |
| Baseboard / base molding | Linear feet | +10% (corners, joints) | 220 LF molding |
| Crown molding | Linear feet | +15% (compound miters) | 230 LF molding |
| Landscape edging | Linear feet | +5% | 210 LF edging |
| Gutters | Linear feet | +10% (miters, outlets) | 220 LF gutter material |
| Wallpaper border | Linear feet | +15% (pattern matching) | 230 LF border |
Frequently Asked Questions
Measure each wall at floor level. Sum all wall measurements. Subtract each doorway width (typically 32–36 inches). Add 10% for corner cuts and joints: Total baseboard = (sum of walls − doorways) × 1.10. Example: room 12×16 ft with one door (34 inches): Perimeter = 2(12+16) = 56 ft. Minus door: 56 − 2.83 ft = 53.17 ft. With 10% waste: 53.17 × 1.10 = 58.5 linear feet of baseboard — order 60 linear feet.
Circumference is the perimeter of a circle specifically — it is the technical term for the distance around a circular boundary. Perimeter is the general term for the distance around any closed shape. Formula: circumference = 2πr = πd, where r = radius and d = diameter. A circular garden bed with 10-foot diameter has a circumference (perimeter) of π × 10 = 31.4 linear feet of edging needed.
Measure every wall segment individually and sum them. For an L-shaped room, you will have 6 wall segments (two long sides, two short sides, and two additional segments from the L notch). Example: 6 + 10 + 6 + 4 + 12 + 14 = 52 linear feet. This is the same regardless of how you conceptually split the L — the physical perimeter is just the total of all wall lengths measured around the boundary.
A square 1-acre lot is approximately 208.7 × 208.7 feet, giving a perimeter of approximately 835 linear feet. A rectangular 1-acre lot (100 × 435.6 ft) has a perimeter of approximately 1,071 linear feet. The more elongated the lot shape, the longer the perimeter for the same area — a 1-acre lot can have widely varying fencing requirements depending on its shape. Always measure the actual boundary rather than estimating from acreage alone.
Crown molding requires the highest waste factor of any trim material — 15–20% is appropriate. The reason: crown molding requires compound miter cuts at inside corners (two simultaneous angle cuts), and cutting practice pieces to set up the saw angles correctly uses material. Additionally, crown molding must be long enough to span each wall without intermediate joints on visible walls. Buy in long lengths (16 ft when available) and factor 15% waste into your linear footage calculation.
Walk the property boundary and measure each straight segment with a measuring tape or measuring wheel. Sum all segments. For curved boundaries, use a measuring wheel along the actual curve — a straight-line measurement underestimates the curved length. If you have a survey plat, the boundary distances are listed and can be summed directly. Property corners are typically marked with iron stakes or pins that can be located using a metal detector if not visible above grade.