# efficiency

/ɪˈfɪʃənsi/ (US) · /ɪfˈɪʃənsi/ (UK)

Source: https://englishreference.com/word/efficiency
Updated: 2026-06-19

## Senses

### 1. avoiding waste

noun · CEFR B2

the ability to do something well and quickly without wasting time, money, or energy.

For teachers: the state or quality of being efficient; the ability to achieve maximum productivity with minimum wasted effort or expense.

- The new heating system has much better energy efficiency than the old one.
- The consultancy firm was hired to improve the operational efficiency of the factory by streamlining the assembly line process.

Usage: Often used with the preposition 'of' when referring to a specific resource, such as 'efficiency of fuel'.

### 2. physics/engineering

noun · CEFR C1 · Technical

the ratio of useful work or energy produced compared to the energy put in.

For teachers: the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in.

- Most car engines have a thermal efficiency of only about twenty-five percent.
- Engineers are constantly seeking to increase the aerodynamic efficiency of the aircraft to reduce fuel consumption during long-haul flights.

Usage: Usually expressed as a percentage or a decimal between 0 and 1.

### 3. a small apartment

noun · CEFR C1 · American English

a small apartment that usually has only one main room for living and sleeping.

For teachers: a small, self-contained apartment, typically consisting of a single main room with a small kitchen area and a bathroom.

- He rented a small efficiency near the university to save money on rent.
- The building offers several efficiencies that are ideal for single professionals who prioritize a central location over square footage.

Usage: Commonly used in real estate listings in the United States.

Teaching tip: Learners should note that 'studio apartment' is more common globally, while 'efficiency' is specifically American.

### 4. power to produce an effect

noun · CEFR C2 · Archaic · Formal

the power or ability to produce a specific result.

For teachers: the capacity or power to produce a desired effect or result.

- The old books spoke of the efficiency of certain herbs in curing fevers.
- The philosopher questioned the efficiency of the law in truly changing human behaviour rather than merely punishing it.

Usage: In modern English, 'efficacy' is almost always preferred for this meaning.

Teaching tip: This sense is rarely encountered in modern speech; advise students to use 'efficacy' for the power of a medicine or treatment.

## Examples

- The new engine has much better fuel efficiency.
- The manager introduced a new software system to improve the efficiency of the office and reduce paper waste.
- While the factory's mechanical efficiency is high, the overall profitability remains low due to the rising costs of raw materials and international shipping logistics.

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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.