per

The word per is a versatile preposition that serves as a fundamental building block in the English language for expressing ratios, distributions, and rates. At its core, it functions as a synonym for 'for each' or 'for every', allowing speakers to link two different units of measurement or conceptual categories. Whether you are discussing the speed of a vehicle, the cost of groceries, or the frequency of a habit, per provides a concise way to establish a mathematical or logical relationship between a numerator and a denominator. In modern usage, it has transcended its purely mathematical origins to become a staple of both professional correspondence and casual conversation.

Mathematical Ratio

Used to indicate a rate or amount in relation to a single unit, such as miles per hour or dollars per gallon.

Distributive Frequency

Used to describe how often something happens within a specific timeframe, like three meals per day or twice per week.

Formal Correspondence

Often used in the phrase 'as per' to mean 'according to' or 'in accordance with' instructions or agreements.

In professional settings, you will frequently encounter per in financial reports and legal documents. Phrases like 'income per capita' or 'cost per unit' are essential for analyzing economic data. Interestingly, while per is often associated with formal or technical contexts, it is equally common in everyday life. When you go to the gym, you might aim for a certain number of heartbeats per minute. When you buy fruit, you check the price per kilogram. This ubiquity makes it one of the most useful prepositions for learners to master, as it bridges the gap between basic arithmetic and complex descriptive language.

Furthermore, the word has a historical depth that informs its current usage. Derived from Latin, it originally meant 'through' or 'by means of'. This heritage is still visible in phrases like 'per cent' (by the hundred) or 'per annum' (by the year). Understanding this 'through' connection helps clarify why we use it to measure things moving through time or space. It acts as a conduit between the quantity and the scale. For instance, when we say 'one apple per child', we are conceptually passing one apple through the filter of each individual child in the group.

Scientific Precision

In physics and chemistry, 'per' is used to define constants and variables, such as grams per mole or meters per second squared.

Using per correctly requires an understanding of how to balance two nouns or a noun and a measurement. The most common structure is [Quantity] + [Unit] + per + [Reference Unit]. For example, '50 miles per hour'. Here, '50 miles' is the quantity, and 'hour' is the reference unit. It is important to note that the reference unit following per is almost always singular, even if the meaning implies a plural group. We say 'per person', not 'per people', and 'per day', not 'per days'. This singular usage emphasizes the individual nature of the distribution.

The 'As Per' Construction

This is a common business idiom meaning 'according to'. Example: 'As per your request, I have attached the file.' Some grammarians find this redundant and prefer just 'per' or 'according to', but 'as per' remains standard in corporate English.

Pricing and Commerce

In retail, 'per' links the price to the weight or count. Example: '$2.99 per pound' or '$10 per dozen'. It provides a clear standard for comparison across different products.

Another critical usage involves statistics and demographics. When researchers talk about 'per capita' income, they are dividing the total income of a country by its total population. This allows for a fair comparison between large and small nations. Similarly, 'per cent' literally means 'per hundred', which is why we use the '%' symbol to represent parts of a whole. When you say '50 per cent', you are saying '50 for every 100'. This conceptual framework is vital for understanding probability, interest rates, and statistical significance in any academic or professional field.

In more advanced writing, per can be used to indicate the means by which something is sent or delivered, though this is becoming rarer. For instance, 'sent per post' or 'delivered per courier'. In these cases, it functions similarly to 'by'. However, in modern English, 'by' is usually preferred for transport or delivery, while per is strictly reserved for rates and ratios. If you want to sound modern and natural, stick to using per for measurements and 'as per' for following instructions.

Frequency in Habits

You can use 'per' to describe your routine. Example: 'I go to the gym four times per week.' This sounds slightly more formal than 'four times a week'.

You will hear per in a wide variety of real-world scenarios, ranging from the mundane to the highly technical. One of the most common places is in a car or on public transport. Speedometers and traffic signs frequently use 'miles per hour' (mph) or 'kilometers per hour' (km/h). When a driver is pulled over by the police, the officer might say, 'Do you know you were doing eighty miles per hour in a sixty-mile zone?' In this context, the word is used to enforce safety standards and legal limits. It provides a standardized way to talk about movement through space over time.

In the Grocery Store

Price tags are the most frequent place to see 'per'. You'll see '$4.00 per lb' or '€2.50 per kg'. Shoppers use these 'per' units to determine which product offers the best value for money.

In the Workplace

Managers use 'per' to discuss productivity and deadlines. 'We need to process fifty applications per day' or 'The budget allows for ten dollars per employee for the holiday party.'

In the world of finance and economics, per is unavoidable. News anchors often report on 'earnings per share' or 'GDP per capita'. These metrics are the lifeblood of market analysis. If a company reports that its profit per share has dropped, its stock price might fall. Similarly, when discussing climate change, scientists often talk about 'parts per million' (ppm) of carbon dioxide in the atmosphere. Here, per is used to describe incredibly small concentrations that have massive global impacts. It allows us to quantify the invisible and the abstract.

You will also hear per in the context of sports and gaming. Commentators might mention a player's 'points per game' or 'yards per carry'. In video games, players often discuss 'frames per second' (FPS) to describe the smoothness of the graphics. In all these cases, per serves as the bridge that turns a raw number into a meaningful performance metric. It tells you not just how much happened, but how efficient or consistent that action was over a specific period or attempt.

In Legal Documents

Lawyers use 'per' to define terms of service or penalties. 'A fine of fifty dollars per day will be applied to late payments.'

While per is a relatively simple word, it is often the source of grammatical errors, particularly for non-native speakers. The most frequent mistake is the addition of an unnecessary article (a, an, or the) after per. Because per already implies 'for each', adding 'a' is redundant. For example, saying 'sixty miles per an hour' is incorrect; the correct form is 'sixty miles per hour'. This is a subtle point, as in other constructions we would say 'sixty miles an hour'. The word per replaces the need for the article entirely.

Pluralization Errors

Another common error is pluralizing the noun that follows 'per'. Learners often say 'five dollars per persons' or 'twice per weeks'. In English, the unit following 'per' should almost always be singular because 'per' focuses on the individual unit of measurement. The correct versions are 'five dollars per person' and 'twice per week'.

Redundancy with 'As Per'

Many people use 'as per' when they only need 'per' or 'according to'. While 'as per' is common in business, phrases like 'as per your instructions' can be simplified to 'per your instructions'. Using 'as per' too frequently can make your writing sound overly bureaucratic or stiff.

Confusing per with 'pre' or 'pro' is another mistake, though usually limited to spelling or very early learners. 'Pre' means before, and 'pro' means for or in favor of. Per is strictly about ratios and means. Additionally, some learners use per when they should use 'by'. For example, 'I sent it per email' is technically understandable but 'I sent it by email' is much more natural in modern English. Per should be reserved for rates (how much of X for every Y) rather than the medium of communication.

Finally, there is the 'per' vs. 'a/an' dilemma. While they often mean the same thing, they are not always interchangeable in tone. 'Sixty miles an hour' is perfect for a story or a conversation. 'Sixty miles per hour' is better for a technical manual or a police report. Using 'per' in a very casual setting can sometimes make you sound like you are trying too hard to be formal. Conversely, using 'a' in a scientific paper might make the writing seem slightly less precise. Choosing the right one depends entirely on your audience and the level of formality required.

Misusing 'As Per' as a general adverb

'As per' should be followed by a noun (like 'as per the rules'), not used as a standalone phrase like 'as per usual' (though 'as per usual' is a common idiom, it is technically redundant).

Understanding the alternatives to per can help you vary your language and match the tone of your environment. The most common alternative is the simple article 'a' or 'an'. In many everyday contexts, 'a' is actually more natural than per. For instance, 'I work forty hours a week' sounds more conversational than 'I work forty hours per week'. However, 'per' is the go-to choice for formal, technical, or scientific writing where precision is paramount. It signals that you are providing a specific rate or ratio rather than just a general description.

'Per' vs. 'Each'

'Each' is often used when the focus is on the individual items themselves. 'The apples are fifty cents each.' 'Per' is used when linking two different units. 'The apples are two dollars per kilogram.' Use 'each' for counts and 'per' for ratios.

'Per' vs. 'According to'

In the context of 'as per', 'according to' is a more common and often clearer alternative. 'According to the manual' is slightly less formal than 'as per the manual'. If you want to sound approachable, use 'according to'.

'Per' vs. 'By'

'By' is used for the method of doing something. 'Sent by mail'. 'Per' is used for the rate. 'Five dollars per letter'. While 'per' was historically used for methods, it is now almost exclusively for rates.

In technical fields, you might also see 'for every' used as a more descriptive alternative. 'For every ten people, there is one car' is a more narrative way of saying '0.1 cars per person'. Using 'for every' can make complex statistics easier for a general audience to visualize. Another alternative in business is 'pro rata', which means 'in proportion'. While 'per' gives you the rate, 'pro rata' describes the process of calculating something based on that rate. For example, 'If you work half the month, you will be paid pro rata'.

Finally, when discussing time, 'a' is almost always preferred in British English for casual frequency ('twice a week'), whereas 'per' is seen as more international or American in those same casual contexts. However, in the UK, 'per' is still the absolute standard for 'miles per hour'. Understanding these subtle shifts in preference helps you sound more like a native speaker. When in doubt, use 'a' for casual time and 'per' for everything else involving numbers and measurements.

'Per' vs. 'In'

Sometimes 'in' is used for proportions, like 'one in ten'. This is different from 'per'. 'One in ten' describes a subset of a group, while 'one per ten' would describe a ratio of one thing assigned to every ten of another.