Rivet Size Calculator: Diameter, Length & Type

Rivet Size Calculator

A rivet size calculator is a tool that recommends a rivet diameter, length, and material type from the size of the hole, the thickness of the material, and the grip range of the joint. A rivet is a short metal pin that joins two or more layers of material by forming a head on each end, one factory-made and one formed during installation. Picking the wrong size can leave the joint weak or stop the rivet from fitting at all.

How Rivet Diameter Is Calculated

The rivet has to pass through the pre-drilled hole, so its diameter can never be larger than the hole. In practice a hole is drilled about 0.1 mm to 0.3 mm larger than the rivet body, to let it slide in easily.

The calculator works from a set of standard metric rivet diameters: 2.4, 3.2, 4.0, 4.8, and 6.4 millimeters. It picks the largest of these that still fits the hole.

Formula:

$\text{Rivet Diameter} = \text{largest standard size} \leq \text{Hole Diameter}$

For example, a 4.2 mm hole fits a 4.0 mm rivet (the next size up, 4.8 mm, is too big). A hole smaller than 2.4 mm cannot take any standard rivet, so the calculator shows an error instead of guessing.

Checking shear strength

A thin rivet in a thick material can shear off under load. As a rule of thumb, the rivet diameter should be at least three times the combined thickness of the material being joined:

$\text{Minimum Diameter for Shear Strength} = 3 \times \text{Material Thickness}$

If the hole is too small to allow a rivet that meets this rule, the calculator still returns the largest rivet that fits the hole, but adds a warning that the joint may be weaker than ideal. Fixing this means drilling a larger hole and using a bigger rivet, or spacing more rivets along the joint to share the load.

How Rivet Length Is Calculated

Rivet length depends on the grip range: the total thickness of every layer being joined. The rivet also needs extra length beyond the grip so its tail can form a head, called the shank allowance. That allowance equals 1.5 times the rivet's own diameter.

Formula:

$\text{Minimum Length} = \text{Grip Range} + 1.5 \times \text{Rivet Diameter}$

The calculator rounds this figure up to the next standard length: 6, 8, 10, 12, 16, 20, or 25 millimeters. If the required length is longer than 25 mm, no standard rivet fits and the calculator returns an error rather than a guess.

Rivet Type and Rivet Code

The recommended rivet material follows the material being joined: aluminum sheet gets an aluminum rivet, steel gets a steel rivet, stainless steel gets a stainless-steel rivet, plastic gets a plastic rivet, and mixed materials get a multi-material rivet. This avoids galvanic corrosion, which happens when two different metals touch in the presence of moisture and the less noble metal corrodes faster.

The calculator also builds a short rivet code for ordering or documentation:

$\text{Rivet Code} = \text{Material Code} + \text{Diameter}\times10 + \text{"-"} + \text{Length}$

The material codes are AL (aluminum), ST (steel), SS (stainless steel), PL (plastic), and MM (multi-material). A 4.0 mm steel rivet, 8 mm long, gets the code ST40-8.

Example

Take a 1.5 mm aluminum sheet with a 3.2 mm hole and a grip range of 3.0 mm.

1. Diameter: the largest standard size at or below 3.2 mm is 3.2 mm itself.
2. Length: minimum length = 3.0 + 1.5 × 3.2 = 7.8 mm, rounded up to the standard 8 mm.
3. Shear check: the rule of thumb calls for a diameter of at least 3 × 1.5 = 4.5 mm, but only 3.2 mm fits the hole, so the calculator flags a shear-strength warning.
4. Result: a 3.2 mm aluminum rivet, 8 mm long, code AL32-8, with a warning to consider a larger hole and rivet.

A second case avoids the warning. A 1.0 mm steel sheet with a 4.2 mm hole and a 2.0 mm grip range gives a 4.0 mm diameter (the largest standard size at or below 4.2 mm), a length of 2.0 + 1.5 × 4.0 = 8.0 mm (already a standard size), and a diameter that clears the 3 × 1.0 = 3.0 mm shear minimum. The result is a 4.0 mm steel rivet, 8 mm long, code ST40-8, with no warning.

Blind Rivets and Solid Rivets

A blind rivet, often called a pop rivet, can be installed from one side of the material only. It has a tubular body and a center pin, called a mandrel, that snaps off once pulled, forming a head on the far side the installer cannot see. A solid rivet needs access to both sides: one end is already shaped like a head, and the other is hammered or pressed flat during installation. Solid rivets generally carry more load for their size but take longer to install.

Common Uses

Riveting joins sheet metal without the heat and warping that welding can cause. Aircraft skins and structural frames use rivets extensively, since they hold up well under repeated vibration. Car bodies, metal roofing and cladding, ladders, and other DIY metalwork use the same fasteners at a smaller scale. Boat hulls and deck fittings often use aluminum or stainless-steel rivets because they resist corrosion in wet conditions better than plain steel.

Bolts, welding, adhesives, and self-tapping screws are common alternatives. Bolts allow the joint to be taken apart later; welding gives a continuous, very strong joint but needs specialized equipment; adhesives spread the load evenly but can weaken in heat; self-tapping screws skip the separate hole-drilling step in some materials.

Frequently Asked Questions

What does the rivet code mean? It combines the material (AL, ST, SS, PL, or MM), the diameter in tenths of a millimeter, and the length in millimeters. AL32-8 is an aluminum rivet, 3.2 mm in diameter and 8 mm long.

Why did the calculator warn me about shear strength even though it gave me a result? The hole limited the rivet to a diameter smaller than three times the material thickness. The calculator still returns the largest rivet that fits the hole, since that is the only rivet that will physically go in, but the warning means the joint may not carry as much load as it should.

Can I use aluminum rivets on steel, or steel rivets on aluminum? It works mechanically, but the two metals can corrode where they touch, especially outdoors or near salt water. Stainless-steel rivets are a safer choice for joining dissimilar metals.

Why does the calculator show an error instead of a size? Two situations produce an error: a hole smaller than 2.4 mm, since no standard rivet is that thin, and a grip range so large that even the biggest rivet, 6.4 mm, would need a length over 25 mm, the longest standard size.

What is grip range? Grip range is the combined thickness of every layer the rivet passes through. It sets how much of the rivet's length sits inside the material before the shank allowance for forming the head.

How much longer than the grip range should a rivet be? About 1.5 times its own diameter, rounded up to the nearest standard length. A 4.0 mm rivet needs roughly 6 mm of extra length beyond the grip range to form its head properly.

References

1. Higgins, Raymond A. (2001). Materials for Engineers and Technicians. Newnes. ISBN 978-0750652506.
2. Messler, Robert W. (2004). Joining of Materials and Structures: From Pragmatic Process to Enabling Technology. Butterworth-Heinemann. ISBN 978-0750677578.
3. ASME B18.1.1: Small Solid Rivets. American Society of Mechanical Engineers.
4. ISO 14588: Blind rivets — Terminology and definitions. International Organization for Standardization.