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Preposition before noun

In depth or of depth?

In depth is a standard expression meaning thoroughly or in great detail. Of depth is uncommon and usually appears only in specialised descriptions.

Quick answer

Which expression is correct?

Use in depth to mean thoroughly or in detail: an in-depth analysis or discuss something in depth. Of depth is not a normal alternative in this meaning, though it may appear in technical phrases such as measurement of depth.

We discussed the issue in depth.
The report provides an in-depth review.
The engineer recorded the measurement of depth at several points.

Choose the pattern by meaning

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

1
in depth

Talking about detailed discussion or study

In depth functions as an adverbial phrase meaning thoroughly.

The topic was examined in depth during the seminar.
They spoke in depth about the proposal.
2
in-depth + noun

Using the adjective form

Hyphenate in-depth before a noun.

She wrote an in-depth analysis of the market.
The course includes an in-depth study of climate policy.
3
depth of + noun

Referring to how deep something is

Depth commonly takes of before a noun phrase.

Scientists measured the depth of the river carefully.
We were surprised by the depth of his knowledge.

See the difference in context

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

Construction
Example
Meaning
in depth
The team discussed the problem in depth.
Standard expression meaning thoroughly or in detail.
in-depth
She gave an in-depth explanation.
Adjective before a noun.
of depth
The measurement of depth was inaccurate.
Possible only when of belongs to another noun such as measurement.
depth of
The depth of the lake is unknown.
Standard way to describe how deep something is.

Common mistakes

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

Using of depth instead of in depth

Of depth does not normally mean thoroughly.

✕ We analysed the issue of depth. ✓ We analysed the issue in depth.

Missing the hyphen before a noun

Use a hyphen in the adjective form before a noun.

✕ an in depth report ✓ an in-depth report

Using in-depth after a verb

After a verb, the adverbial phrase is usually in depth without a hyphen.

✕ They discussed it in-depth. ✓ They discussed it in depth.

Confusing depth of with of depth

Depth normally comes before of.

✕ the of depth measurement ✓ the depth measurement

Quick practice

Choose the expression that matches the intended meaning.

1. The article examines the issue ___ depth.
2. She wrote an ___ report on urban planning.
3. The divers measured the ___ the cave.

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Frequently asked questions

Is in depth always two words?

Yes when used after a verb. Before a noun, use the hyphenated form in-depth.

Can of depth mean detailed?

No. English uses in depth or in-depth for that meaning.

What does depth of mean?

It refers to how deep something is, physically or metaphorically.

"in act" or "of act"? "in agreement" or "of agreement"? "in appearance" or "of appearance"? "in area" or "of area"? in, at, on, of or to hand? "in attempt" or "of attempt"? "in battle" or "of battle"? "in celebration", "of celebration" or "for celebration"? "in chain" or "of chain"? "in chapter" or "of chapter"? "in charge" or "of charge"? "in check" or "of check"?

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