Ordering a silicone hose online comes down to one thing: getting the size right. Buy the correct bore and length and it slips straight onto the spigot for a clean, leak-free fit; get it wrong and you are left with a hose that either will not go on or slides about with no grip. The good news is that measuring a hose is quick and needs nothing more exotic than a rule or a set of calipers. This guide walks through exactly what to measure, how to measure it, and the small details that catch people out — so you can order from our silicone hose range with confidence.
The three measurements that matter
Every silicone hose is defined by three figures: the bore (the internal diameter, i.e. the hole the fluid flows through), the length, and the wall thickness. Of these, the bore is by far the most important, because it is the dimension that has to match your engine's spigots. On our site every hose is listed by its internal bore, so once you know that number you are most of the way there. Length matters for straights and custom runs, while wall thickness is usually fixed by the hose specification you choose. Get the bore right first, then confirm the length and shape.
How to measure the bore (internal diameter)
The bore is the internal diameter, measured across the inside of the hose end from wall to wall. The easiest and most accurate way is with a vernier or digital caliper: open the jaws inside the hose end and read off the internal measurement. If you do not have calipers, lay the hose end flat and measure the internal opening with a steel rule, or measure the outside diameter of the metal spigot the hose needs to fit over — that spigot's outer diameter is effectively the bore you need. Always work in millimetres for accuracy, and never order by the outside diameter of the old hose, because wall thickness varies and you will end up with the wrong size.
How to measure the length
For a straight hose, measure end to end along the hose. The important rule is to measure along the centreline, following any curve rather than taking a straight-line shortcut, so that the hose you order actually reaches. It is usually wise to allow a little extra and trim to fit on installation rather than ordering short. Remember that a hose needs to push fully onto the spigot at each end, so factor in that seating length when you work out how much hose you actually need between two fixed points.
Measuring different shapes: straights, elbows and reducers
Not every hose is a simple straight. A silicone reducer steps between two different bores, so you need to record the internal diameter at each end separately — for example 51mm down to 45mm. A silicone elbow turns a corner, so as well as the bore you should note the angle (commonly 45, 90 or 135 degrees) and the length of each leg measured from the centre of the bend. A coupler or joiner is a short straight used to connect two pipes of the same size. Knowing which shape you need before you measure makes ordering far simpler.
Wall thickness and ply
Wall thickness is the third dimension, and while you rarely need to measure it yourself, it is worth understanding. A thicker wall and more reinforcing plies mean a hose that resists higher pressure and holds its shape better under boost, which is why intercooler and induction hoses tend to be more heavily reinforced than a simple low-pressure coolant hose. When you choose a hose specification from our range the appropriate wall and ply are already built in, so you do not need to calculate it — just be aware that a heavier-duty hose will have a slightly larger outside diameter for the same bore, which affects clamp sizing.
Sizing your clamps
Once you have the hose, the clamp is sized to the outside diameter of the hose after it is pushed fully onto the spigot — not the bore. This is the one place the outside diameter genuinely matters. As a rough guide, add roughly twice the wall thickness to the bore to estimate the outer diameter, then choose a clamp whose range comfortably covers it. Our worm-drive hose clips suit standard coolant joints, while T-bolt clamps are the choice for boost and induction work. Browse the full hose clips and clamps range to match the right clamp to your hose.
Still not sure? We can help
If your exact size is not listed, you have options. Round to the nearest listed bore for a snug, workable fit; use a reducer where two ends differ; or, for a vehicle we already cover, fit one of our pre-shaped vehicle-specific hose kits and skip the measuring altogether. And if nothing standard suits, get in touch — we manufacture custom silicone hoses in-house and can often produce a bespoke bore, length or shape to order. Measure twice, order once, and the job goes smoothly.
Frequently asked questions
How do I measure the bore of a silicone hose?
Measure the internal diameter (the hole the fluid flows through), not the outside. Measure across the inside of the hose end with a vernier caliper or a steel rule, and match that figure to the bore size on the product page. Our hoses are always listed by their internal bore.
Should I measure the inside or outside diameter?
Always order by the internal diameter (bore), because that is the size that has to match your engine's spigots. The outside diameter only matters when you are choosing a clamp, which is sized to the hose's outer diameter once it is pushed onto the spigot.
How do I measure a hose that is bent or curved?
Measure the length along the centreline of the hose following the curve, not in a straight line from end to end. For elbows, note the leg lengths from the centre of the bend, and for reducers record the bore at each end separately.
What if my exact size is not listed?
Round to the nearest listed bore for a snug fit, choose a reducer if the two ends differ, or get in touch. We manufacture custom silicone hoses and can often make a bespoke size or shape if a standard part will not fit.
