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How to find radiator hose size?

To determine radiator hose size, measure the hose’s inner diameter and compare it to the fittings, or check official specifications. This ensures you buy the right hose and clamps.

Why hose size matters

Size affects fit, coolant flow, and the reliability of the cooling system. An undersized hose can restrict flow and overheat, while an oversized hose may not seal properly with a clamp. Getting the correct size is essential for long-term performance.

Direct measurement of the hose ID

To measure accurately, remove the hose from the vehicle if possible and measure its inner diameter with calipers or a ruler. This measurement is the size you need to match to the radiator and engine fittings.

Ensure the engine is cool and depressurized before starting.

Use a caliper to measure the inside diameter (ID) across the bore, or a flexible ruler if a caliper isn’t available.

Record the measurement in inches or millimeters, noting that most hoses are sized by ID rather than outer diameter (OD).

Compare the measured ID to available hoses in the parts catalog or retailer listings to find an exact match.

Direct measurement provides the most precise size, but it requires access to the hose and the appropriate measuring tools.

Using OEM specifications and markings

Hoses often carry size information or part numbers stamped on the outer surface, and vehicle service manuals or OEM diagrams list the required hose size. Referring to these sources reduces guesswork, especially for models with unique cooling-system layouts.

Look for markings on the hose, such as "1.25 in" or "32 mm."

Check the vehicle’s owner manual, service manual, or official parts catalogs for hose size specs.

Cross-check the OEM part number with retailer listings to confirm fitment for your exact engine and model year.

If replacing the hose on a vehicle with varying ends, verify sizes at both ends since inlet/outlet diameters may differ.

OEM references and markings provide authoritative guidance and are especially reliable for specialty or performance applications.

Common size ranges and practical tips

In passenger cars, radiator hose inner diameters typically range from roughly 16 mm (5/8 in) to 44 mm (1-3/4 in). Trucks and SUVs can exceed 45 mm (2 in) in certain configurations. When ordering, focus on the inner diameter (ID) and the distance between hose ends, then confirm clamp size compatibility and material (rubber, silicone, heat resistance). If in doubt, bring the old hose or a tape measure to the parts counter for assistance.

Where to look on the hose and fittings

Hose markings or part numbers can be printed on the outer surface. Fittings and clamps may have their own size requirements indicated on packaging or manuals. If marks are hard to locate, record the end-to-end length and end diameters to help match a replacement.

Summary

Finding radiator hose size hinges on identifying the inner diameter, verifying with OEM specs, and considering both ends of the hose. Direct measurement, cross-referencing service manuals, and reading markings on the hose all help ensure you select the correct size and compatible clamps. When in doubt, consult a parts specialist or refer to model-specific repair guides for precision guidance.

How do I know if my hose is 5'8

Now here is where the two different hose sizes come into play the spot tap is a 3/4 in pipe it uses a standard garden hose thread. And if we connect a 3/4 in hose to that head the majority of the

How to measure radiator hose size?

To measure a radiator hose, first measure the inside diameter for the size and the length from the ends of the hose where it will connect. Measure the inside diameter by placing a ruler or calipers across the opening of the hose, and measure the length by laying the hose straight and marking where it needs to be cut.

Measure the inside diameter

For replacement hoses: Measure the outside diameter of the pipe or tube the hose will connect to. For most soft hoses, the inside diameter will be the same as the pipe's outside diameter.
For the old hose: Use a ruler or measuring tape to find the straight distance across the inner opening of the hose.

This video explains how to measure the inside and outside diameter of a hose: 1mCar Builder SolutionsYouTube · Jan 28, 2014
Measure the length

With the hose in place: Run a piece of tape around the hose to mark the approximate length and bend it to follow the path from the engine to the radiator. Note the total length, including any bends.
After removing the old hose: Lay the old hose straight. Place a piece of tape at each end of the hose to indicate the required length. Measure the distance between the two pieces of tape.
For custom hose assemblies: Use a piece of flexible wire to mock up the path from the engine to the radiator. Measure the length of the wire, transferring the measurements to the hose.

You can watch this video to learn how to install and measure a custom radiator hose: 1mFast Monty's GarageYouTube · Oct 17, 2020
What to look for

Cracks or deterioration: Check the old hose for any signs of damage, such as cracks, brittleness, or soft spots. If you find any, it's time to replace it.
Hose clamps: Ensure that the hose is properly secured to the radiator and engine with clamps. If you're using a custom hose assembly, make sure the clamps are tight and secure.

How to identify a radiator hose?

Radiator hoses are the largest hoses in the engine's cooling system, typically consisting of an upper hose running from the engine's thermostat to the radiator and a lower hose connecting the radiator to the water pump. They are large, flexible rubber hoses located at the front of the vehicle, and they can be identified by their connection to both the radiator and the engine.
You can watch this video to see an example of a radiator hose in a car engine: 1mAutOdometerYouTube · Mar 28, 2017
How to identify radiator hoses

Locate the radiator: This is typically at the front of the car.
Look for large hoses connected to it: The radiator has two main hoses that are significantly larger than other hoses in the engine bay.
Follow the hoses to the engine:
- The upper radiator hose connects the engine's thermostat housing to the top of the radiator. You can often see this one most clearly from the front or the top of the engine.
- The lower radiator hose connects the bottom of the radiator to the water pump, which is often on the side or front of the engine and driven by the serpentine belt. This hose can be harder to see and may require you to look under the car.
Differentiate from heater hoses: Radiator hoses are much larger than the smaller "heater hoses" which connect to the heater core located inside the car's dashboard.
Look for specific connections: Some radiator hoses are molded into a "T" shape with other hoses branching off, while some modern vehicles may have composite or plastic coolant lines.

This video shows the location of different hoses in the engine bay and how to distinguish between them: 47sehowautoYouTube · May 21, 2015

How do I tell what size hose I have?

To find your hose size, measure the inside diameter (ID) of the hose using calipers or a ruler. For garden hoses, common sizes are 1/2"1 / 2 "1/2", 5/8"5 / 8 "5/8", and 3/4"3 / 4 "3/4". For industrial or hydraulic hoses, you may need to check the hose's lay line for a printed ID, or convert a "dash size" (e.g., -12 for 3/4"3 / 4 "3/4") to its fraction equivalent.

For garden hoses
This video demonstrates how to measure the inside diameter of a garden hose: 52sMagnetsAndMotors (Dr. B's Other Channel)YouTube · Dec 21, 2024

Measure the inside diameter: Use a ruler or measuring tape to measure the distance across the inner opening of the hose's end.
Look for printed numbers: Many garden hoses have the size printed on them, such as "1/2"1 / 2 "1/2", "5/8"5 / 8 "5/8", or "3/4"3 / 4 "3/4". The most common size is 5/8"5 / 8 "5/8", note this YouTube video.
Compare to a reference: Line up hoses of different sizes to see the difference in their inner diameters, as shown in this YouTube video.

For industrial and hydraulic hoses

Check the lay line: Look for printed information directly on the hose cover. This "lay line" will often include the size in a standard format, such as a fraction (e.g., 3/4"3 / 4 "3/4") or a "dash size".
Understand dash sizes: In hydraulic hoses, the size is often expressed as a dash size, which is the ID in 1/16ths of an inch. For example, a 3/4"3 / 4 "3/4" ID hose has a dash size of "-12" (3/43 / 43/4 is equal to 12/1612 / 1612/16).
Measure the inside diameter: If the lay line is not readable, use calipers to accurately measure the inside diameter.
Check the fittings: For some specialty hoses, like AN fittings, the size is based on the male thread's outer diameter or female thread's inner diameter.

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.