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Prepositions before nouns

“Of unit” or “per unit”?

Per unit is the standard expression for rates, prices, or measurements. Of unit is not a normal standalone English combination.

Quick answer

Use “per unit” for rates and measurements

Use per unit when giving a price, amount, or measurement for each item. The phrase of unit is generally not idiomatic unless unit is part of a longer noun phrase such as size of unit.

The cost is $5 per unit.
Energy consumption per unit decreased this year.
The size of the unit was too small.

Choose the pattern by meaning

These forms are not interchangeable. Choose the construction by meaning, not by which preposition appears most often.

1
per unit

Rates, costs, and measurements

Use per unit to mean for each item or measurement unit.

The factory produces 200 items per unit of time.
The charge per unit is reasonable.
2
cost per unit

Business and accounting language

This is a common phrase in finance and production.

The cost per unit fell after automation.
3
units of + measurement

Measurement expressions

English usually uses units of rather than of unit.

The recipe uses two units of measurement.

See the difference in context

The same subject can take different constructions because each sentence answers a different question.

Construction
Example
Meaning
per unit
The company earns a profit per unit.
for each item or measurement
of unit
The size of the unit was unclear.
of belongs to the larger phrase; of unit alone is not idiomatic
cost per unit
We reduced the cost per unit.
standard business expression
unit of measurement
A metre is a unit of measurement.
describes a category or function

Common mistakes

Some combinations appear in real text but do not mean what learners often assume.

Using of unit instead of per unit

Use per unit for rates and calculations.

✕ price of unit ✓ price per unit

Dropping per in measurement phrases

Per is needed to express each item.

✕ $10 unit ✓ $10 per unit

Using unit of when meaning each item

Unit of introduces a category, not a rate.

✕ cost unit of product ✓ cost per unit of product

Using of unit as a fixed phrase

English normally needs a larger noun phrase.

✕ efficiency of unit ✓ efficiency of the unit

Quick practice

Choose the expression that matches the intended meaning.

1. The price is €3 ___ unit.
2. A kilogram is a unit ___ measurement.
3. We reduced the cost ___ unit.

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Frequently asked questions

Is of unit correct English?

Not usually as a fixed phrase. English normally uses a larger structure such as part of the unit or size of the unit.

What does per unit mean?

It means for each individual item, amount, or measurement unit.

Can per unit be used outside business English?

Yes. It is also common in science, engineering, and statistics.

of, about, against, to or for racism? of, about, for, in or on friendship? of, about, for, on or to thing? of, about, for, to or with sex? of, about, on, to or for moon? "of access" or "with access"? "of accommodation" or "for accommodation"? "of accuracy" or "for accuracy"? "of action" or "in action"? "of actor", "with actor" or "by actor"? "of address" or "to address"? "of administration" or "in administration"?

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