How many centimetres in an inch?

Exactly 2.54 centimetres, or 25.4 millimetres. It is a defined value rather than a rounded one.

How do I convert fractions of an inch?

A quarter is 0.25, a half is 0.5, three quarters is 0.75, and eighths go 0.125, 0.375, 0.625 and 0.875. Use the dropdown above rather than typing a decimal.

Is a half inch pipe really half an inch?

No. It is a name from an old standard, not a measurement. The outside is larger and the bore inside is smaller, depending on the material and pressure rating.

What is half inch pipe in millimetres?

In the PPR used in most UAE buildings, a plumber saying half inch usually means a 20 mm outside diameter pipe, and the actual bore inside it is smaller again.

Should I work in inches or millimetres?

Millimetres for anything precise. No fractions, no decimals, and it matches every drawing and material specification here.

How many millimetres in an inch?

25.4 exactly. So three inches is 76.2 millimetres and six inches is 152.4.

Inch to CM Converter

Which way

Whole inches

Fraction of an inch

Centimetres

Use this box when converting the other way.

Your answer

In centimetres

8.89 cm

That is 88.9 millimetres.

In millimetres: 88.9 mm
In metres: 0.0889 m
Total inches: 3.5 in
Whole inches: 3
Fraction: 0.5

One inch is exactly 2.54 centimetres. That is a defined value, not a rounded one.

Inch to CM Converter for Dubai and the UAE

This tool converts between inches and centimetres or millimetres, in both directions.

It also handles fractions of an inch, because that is how small imperial sizes are usually written: a half, a quarter, three quarters.

Inches survive in two places in this metric country: plumbing pipe and screen or appliance sizes. Both come up often enough to be worth a tool.

Where inches still turn up here

A metric country with two stubborn exceptions.

Plumbing pipe
Half inch, three quarter inch and one inch are everyday terms on any plumbing job, even when the pipe itself is metric.
Screens and displays
Televisions, monitors and phones are all measured diagonally in inches, everywhere in the world.
Some appliances
Certain fittings and appliance connections are still specified in imperial threads.
Imported fittings
Anything brought in from a market that uses imperial arrives with imperial sizes on it.
Timber and board
Often described in imperial nominal sizes even though the actual size is metric and smaller.

Pipe inches are not measurements

This is the thing most worth knowing on this page, and it surprises almost everybody.

A half inch pipe is not half an inch across anything. It is a name, not a measurement.

The sizes come from an old standard where the number roughly described the internal bore of a particular wall thickness of iron pipe. Wall thicknesses changed and the names stayed.

So a half inch pipe has an outside diameter somewhat larger than half an inch and an inside diameter somewhat smaller, depending on the material and the pressure rating.

PPR pipe, which is what most UAE buildings use, is sold by outside diameter in millimetres. A twenty millimetre PPR pipe is roughly what a plumber means by half inch, and the actual bore inside it is smaller again.

The practical rule: when somebody says half inch, they mean a size of fitting, not a distance. When you need the actual hole for a flow calculation, look up the bore.

Fractions and why they matter

Imperial sizes go in halves, quarters and eighths rather than in tenths, and that is where conversion errors come from.

Three and a half inches is 3.5. Three and three quarter inches is 3.75, not 3.34 or anything else.

The eighths are the ones people struggle with. One eighth is 0.125, three eighths is 0.375, five eighths is 0.625 and seven eighths is 0.875.

That is why this tool has a dropdown for the fraction rather than asking you to type a decimal. Picking three quarters is harder to get wrong than typing 0.75.

For anything precise, working in millimetres is easier. It avoids fractions entirely and it is what every drawing uses.

Working in millimetres

On a building site here, millimetres are the practical unit and it is worth defaulting to them.

Drawings are in millimetres. Tile sizes are in millimetres. Timber, board, glass and hardware are all specified that way.

There are no fractions and no decimals, which removes a whole class of error. Two thousand four hundred is unambiguous in a way that seven feet ten and a half inches is not.

One inch is 25.4 millimetres, so converting is straightforward.

The one place to be careful is reading a drawing where the unit is not stated. A dimension of 2400 is almost certainly millimetres, but 2.4 could be metres and 240 could be centimetres. If a drawing does not say, ask before cutting anything.

Questions people ask

How many centimetres in an inch?: Exactly 2.54 centimetres, or 25.4 millimetres. It is a defined value rather than a rounded one.
How do I convert fractions of an inch?: A quarter is 0.25, a half is 0.5, three quarters is 0.75, and eighths go 0.125, 0.375, 0.625 and 0.875. Use the dropdown above rather than typing a decimal.
Is a half inch pipe really half an inch?: No. It is a name from an old standard, not a measurement. The outside is larger and the bore inside is smaller, depending on the material and pressure rating.
What is half inch pipe in millimetres?: In the PPR used in most UAE buildings, a plumber saying half inch usually means a 20 mm outside diameter pipe, and the actual bore inside it is smaller again.
Should I work in inches or millimetres?: Millimetres for anything precise. No fractions, no decimals, and it matches every drawing and material specification here.
How many millimetres in an inch?: 25.4 exactly. So three inches is 76.2 millimetres and six inches is 152.4.

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