Perimeter is the single measurement behind every material sold by the running foot — baseboard, crown molding, fencing, gutters, and landscape edging. This calculator handles the common shapes and converts the result straight into a material order with waste allowance.
Need area instead of perimeter? Use the Square Footage Calculator.
About pricing on this page
This calculator is intentionally price-light. Absolute dollar figures are deliberately omitted because they vary too widely by region, brand, and installer to be useful as planning estimates. The relative-comparison tables below show how options stack up against each other — which is the durable, actionable information. For a real budget, get two or three written quotes from local suppliers and contractors after they have seen the job.
Perimeter Calculator
Choose a shape and enter dimensions. Results give perimeter in linear feet plus a material order with waste.
Perimeter Formulas by Shape
Perimeter is the distance around the outside edge of a shape. Unlike area, it is always a single-dimension measurement expressed in linear feet.
| Shape | Perimeter Formula | Example | Result |
|---|---|---|---|
| Rectangle | (Length + Width) × 2 | 14 ft × 12 ft | 52 ft |
| Square | Side × 4 | 12 ft sides | 48 ft |
| Circle | 3.1416 × Diameter | Diameter 12 ft | 37.7 ft |
| Triangle | Side A + Side B + Side C | 10 + 12 + 14 ft | 36 ft |
| L-shape | Sum of all outer sides | See note below | Varies |
| Regular polygon | Side × Number of sides | 8 sides × 5 ft | 40 ft |
An L-shaped room has the same perimeter as the rectangle that encloses it, because the two inset sides equal the two sides they replace. A 20 × 16 room with a 6 × 8 notch removed still has a 72 ft perimeter.
Room Perimeter Reference — Baseboard and Trim
Perimeter drives every trim order. These figures show what to buy for baseboard at three waste levels.
| Room Size | Perimeter (LF) | Less One Door | Order +10% | 8 ft Sticks | 12 ft Sticks |
|---|---|---|---|---|---|
| 8 × 10 ft | 36 | 33 | 37 | 5 | 4 |
| 10 × 10 ft | 40 | 37 | 41 | 6 | 4 |
| 10 × 12 ft | 44 | 41 | 46 | 6 | 4 |
| 12 × 12 ft | 48 | 45 | 50 | 7 | 5 |
| 12 × 14 ft | 52 | 49 | 54 | 7 | 5 |
| 12 × 16 ft | 56 | 53 | 59 | 8 | 5 |
| 14 × 20 ft | 68 | 65 | 72 | 9 | 6 |
| 20 × 20 ft | 80 | 77 | 85 | 11 | 8 |
| 24 × 24 ft | 96 | 93 | 103 | 13 | 9 |
Buying longer sticks means fewer joints in the finished run, which matters visually on long walls. But 16 ft trim will not fit in most vehicles and often cannot turn a stairwell corner.
What Perimeter Is Used For
Every one of these materials is priced and sold by the linear foot, making perimeter the controlling number.
| Material | Typical Cost per LF | Waste Factor | Notes |
|---|---|---|---|
| Baseboard | $1.50–$8 | 10% | Deduct door openings |
| Crown molding | Reference only | 15% | Mitre cuts waste more |
| Quarter round / shoe | $0.75–$3 | 10% | Follows baseboard length |
| Chair rail | Reference only | 10% | Continuous, few deductions |
| Fencing | Reference only | 5% | Deduct gate widths |
| Gutters | Reference only | 5% | Only eave runs, not full perimeter |
| Landscape edging | Reference only | 5% | Curves need more length |
| Paver edge restraint | Reference only | 5% | Full patio perimeter |
Perimeter vs Area — When Each Applies
Mixing these up is the most common estimating error in remodeling, and it produces orders that are wrong by a wide margin.
Use Perimeter for Anything Sold by the Foot
Baseboard, crown molding, chair rail, quarter round, fencing, gutters, countertop edging, and landscape borders are all priced per linear foot. You need the distance around the space, not the surface inside it. A 12 × 14 room needs 52 linear feet of baseboard regardless of how large its 168 square foot floor is.
Use Area for Anything That Covers a Surface
Flooring, tile, paint, drywall, carpet, sod, and mulch all cover a two-dimensional surface and are priced per square foot or square yard. The perimeter of the room tells you nothing useful about how much of these you need. These two numbers answer entirely different questions.
Gutters Use Partial Perimeter, Not Full
A common mistake on gutter estimates is using the full building perimeter. Gutters only run along eave edges, which on a simple gable roof is just two of the four sides. A 30 × 40 ft house has a 140 ft perimeter but only 80 linear feet of gutter if the gables face the sides. Count the actual eave runs from the roof plan.
Deduct Openings From Trim, Not From Fencing Posts
For baseboard, subtract each door opening from the perimeter since no trim crosses it. For fencing, subtract gate widths from the material length but still count the gate posts separately. The deduction affects the material quantity while the post count is driven by the original run length divided by spacing.