# perimeter

/pɝˈɪmətɝ/ (US) · /pəɹˈɪmɪtɐ/ (UK)

Source: https://englishreference.com/word/perimeter
Updated: 2026-06-20

## Senses

### 1. math/geometry

noun · CEFR B1

the total distance around the outside of a shape.

For teachers: the total length of the boundary of a closed two-dimensional figure. Countable in mathematical contexts.

- To find the perimeter of a square, you add the lengths of all four sides together.
- The architect calculated the perimeter of the foundation to determine the exact quantity of concrete required for the retaining wall.

### 2. outer boundary

noun · CEFR B2

the outer edge or border of a specific area, like a building or a park.

For teachers: the outermost limits or boundary of a physical area or complex.

- Security guards patrol the perimeter of the airport every hour.
- The protesters gathered just outside the perimeter of the embassy, held back by a line of temporary steel fencing.

### 3. military defense

noun · CEFR C1 · Technical

a protected line around a military position.

For teachers: a fortified boundary or defensive line established to protect a military installation or position.

- The soldiers worked quickly to secure the perimeter before nightfall.
- The commander ordered the troops to reinforce the western perimeter, fearing that the dense forest provided too much cover for an enemy advance.

### 4. field of vision

noun · CEFR C2 · Technical

a tool used by doctors to measure how far you can see to the sides.

For teachers: an instrument used in ophthalmology to map the extent and sensitivity of a patient's visual field.

- The eye doctor used a perimeter to check if the patient had lost any side vision.
- Automated perimeters have largely replaced manual testing for detecting early signs of glaucoma in clinical practice.

## Examples

- The perimeter of the square garden is twenty meters.
- Security guards patrol the perimeter of the warehouse every hour to check for broken fences.
- Calculating the perimeter of an irregular polygon requires the precise measurement of every individual segment before summing them to find the total boundary length.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.