Hose Clamp Size to Diameter Range Converter

Hose clamps secure flexible hoses onto fittings, pipes, and barbs. They are identified by a size number that corresponds to a specific clamping diameter range. The most common type is the worm gear (or worm drive) clamp, which uses a screw mechanism to tighten a perforated or slotted metal band around the hose.

How hose clamp sizing works: Each size number corresponds to a minimum and maximum clamping diameter. The clamp must be selected so that the hose outer diameter falls within this range. Aim for the middle of a range rather than either edge: wound almost fully out, a worm gear clamp has only a few threads of band still engaged in the screw, and that is where they let go. Wound almost fully in, the surplus band curls up under itself and stops the clamp sitting flat.

Measure over the fitting, not the loose hose. A hose stretched onto a barb or a pipe stub is noticeably larger than the same hose lying on the bench, often by two or three millimetres and sometimes more on thick-walled silicone. Sizing from the loose measurement is the usual reason a clamp turns up too small. The ranges overlap heavily, so being roughly right is normally enough, but not if you measured the wrong thing.

Common hose clamp size reference:

Types of hose clamps:

Worm gear clamps: The most widely available type. A slotted band is tightened by turning a screw that drives a worm gear along the band slots. Advantages include adjustability, reusability, and wide size range. Disadvantages include uneven pressure distribution and the potential for the band edges or screw housing to damage soft hoses.

Spring clamps (constant tension): A spring steel band that provides constant clamping pressure as the hose and fitting expand and contract with temperature changes. Commonly used in automotive cooling systems where temperatures cycle frequently. They require special pliers to install and remove.

T-bolt clamps: A heavy-duty clamp with a T-shaped bolt that draws a thick band tight around the hose. They provide higher clamping force and more even pressure than worm gear clamps. Used in turbocharger intercooler hoses, radiator hoses, and industrial applications where vibration resistance is important.

Ear clamps (Oetiker style): A one-use clamp with one or two “ears” that are crimped flat with a special tool. They provide very even 360-degree clamping pressure and a low profile. Common in automotive fuel lines, power steering lines, and OEM applications.

Material selection: Stainless steel clamps (typically 301 or 304 grade) resist corrosion and are suitable for most applications. Carbon steel (zinc plated) clamps are cheaper but will rust in wet environments. For marine and chemical applications, use 316 stainless steel clamps.