What size is a radiator coolant hose?
There isn't a single universal size for radiator coolant hoses—the inner diameter depends on the vehicle. In practice, most passenger cars use hoses with an inner diameter ranging from about 1/2 inch (12 mm) up to about 1-1/2 inches (38 mm).
The exact size you need varies by whether you're dealing with a radiator hose or a heater-core hose. To replace correctly, measure the hose ID at its widest point or refer to the vehicle’s service data or OEM replacement part number.
Why sizes vary
Radiator and heater-core hoses connect to different fittings, engine blocks, and radiators. The design and coolant flow requirements of each vehicle determine the ID, wall thickness, and flexibility of the hose. As a result, there is no universal size across makes and models.
Typical ranges you may encounter
Use this as a general guide, but verify for your specific vehicle:
- Radiator hoses (upper/lower): commonly around 1/2" to 1-1/2" inner diameter (12–38 mm). Some trucks and performance cars may use larger sizes up to about 2" (50 mm).
- Heater-core hoses: typically about 5/8" to 3/4" inner diameter (16–19 mm).
Sizes vary with engine size and cooling system design; always confirm with measurements or OEM data before purchasing a replacement hose.
How to determine the exact size for your vehicle
To ensure you get the correct hose, measure accurately or verify with the right reference data. The steps below help you identify the correct ID and the right part.
- Let the engine cool completely before touching any coolant hose.
- Remove the hose or slide back the clamp to expose the inside. If you can't remove, measure the hose ID in the middle where it is not deformed.
- Measure the inner diameter with calipers or a ruler. Take the measurement in millimeters and inches; note the closest standard hose size (e.g., 16 mm, 19 mm, 25 mm, 32 mm, 38 mm).
- Check the hose's ends to ensure the inner diameter matches the connecting fittings (hoses taper and clamps may accommodate a small range).
- Refer to the vehicle's service manual or OEM part diagram to confirm the exact size and the corresponding part number.
- If in doubt, bring the old hose to an auto parts store to compare or use the store's fitment system by vehicle year/make/model.
Following these steps will help you select a radiator hose with the correct inner diameter and fit for your cooling system.
Summary
Radiator coolant hose size is not universal. Typical passenger-car hose IDs range from about 12 mm to 38 mm, with heater-core hoses usually smaller. Always confirm by measuring the hose ID or checking OEM data and the vehicle’s service manual before purchasing a replacement.
