Rivet Size Calculator
Enter your material thicknesses and rivet type to get the minimum and recommended shank diameter, required shank length, hole diameter, and spacing guidelines. Results follow the standard 3x-diameter rule for sizing and the 1.5x-diameter allowance for the closing head, consistent with FAA AC 43.13-1B and ISO structural practice. Switch between metric (mm) and imperial (inches) at any time.
How rivet sizing works
Two rules govern almost every riveted joint. First, the minimum shank diameter must be at least three times the thickness of the thickest single plate in the stack. This three-times rule ensures the rivet body can transfer shear without buckling or cracking the surrounding material. Second, the shank must be long enough to span the entire grip (all plates combined) and still leave enough protruding to form a closing head on the back side. That protrusion is typically 1.5 times the rivet diameter for standard button heads, dropping to about 0.5x for flush countersunk heads that need less deformation and rising to 1.7x or 1.8x for pressurized boiler joints that demand a tighter clinch. The computed minimum diameter is then rounded up to the nearest standard stock size, because rivets are only available in discrete diameter increments: 1/32-inch steps in imperial, and the ISO series in metric.
Hole sizing and fit tolerance
The rivet hole must be slightly larger than the shank to allow insertion without splitting the material, but the clearance must be small enough to provide a solid clamp after the rivet is set. Standard practice calls for a hole that is 0.1 mm to 0.25 mm (roughly 0.004" to 0.010") larger than the shank diameter. Aviation repairs governed by FAA AC 43.13-1B use tighter upper limits to avoid loose rivets and fretting. Hole size is normally controlled by the drill bit size: a #30 drill (0.1285") is commonly paired with 5/32" (0.1563") rivets in aluminium airframes, for example. Always verify the specific drill versus rivet pairing in the relevant sizing chart for your material grade and application.
Edge distance, pitch, and row spacing
Two spacing rules prevent tearing and instability in a row of rivets. Edge distance (the distance from a rivet centre to the nearest plate edge) must be at least 2x the rivet diameter for aluminium, 2.5x for steel, and 3x for composite materials that are more prone to bearing-mode failure near free edges. Pitch (centre-to-centre spacing along the row) follows similar multipliers: 4x for aluminium, 4.5x for steel, 5x for composites. These are minimums; structural design may require larger spacing based on load calculations. The transverse pitch (distance between parallel rows) is typically 75% of the longitudinal pitch. Aviation applications additionally specify a maximum pitch of 6x the diameter to avoid inter-rivet buckling of the skin.
Head types and closing-head multipliers
Button (round or universal) heads are the most common general-purpose choice, offering a large bearing area and easy visual inspection of the shop head. Countersunk (flush) heads are used wherever aerodynamic or aesthetic smoothness is needed: the taper angle is usually 100 degrees for aluminium airframes. Flat and pan heads sit between the two, offering a lower profile than button heads without the precision drilling that countersinking requires. The closing-head multiplier controls how much shank protrudes beyond the back of the joint before bucking: button heads need 1.5x, countersunk only 0.5x (because part of the head sits within the material), while boiler and pressurized joints require 1.7-1.8x to form a robust clinch that resists vibration loosening.
Standard rivet sizes and hole tolerances
| Diameter (mm) | Diameter (in / dash) | Min hole (mm) | Max hole (mm) | Typical application |
|---|---|---|---|---|
| 3 | 3/32" (dash 3) | 3.10 | 3.25 | Light sheet metal, electronics |
| 3.5 | 1/8" (dash 4) | 3.60 | 3.75 | Light alloy structures |
| 4 | 5/32" (dash 5) | 4.10 | 4.25 | General automotive & HVAC |
| 4.5 | 3/16" (dash 6) | 4.60 | 4.75 | Medium structural panels |
| 5 | 3/16" (dash 6) | 5.10 | 5.25 | Aircraft skins (light) |
| 6 | 1/4" (dash 8) | 6.10 | 6.25 | Aircraft frames, machinery guards |
| 8 | 5/16" (dash 10) | 8.10 | 8.30 | Heavy structural joints |
| 10 | 3/8" (dash 12) | 10.10 | 10.35 | Boilermaking, bridges |
| 12 | 1/2" (dash 16) | 12.10 | 12.40 | Heavy civil & marine |
| 16 | 5/8" | 16.10 | 16.45 | Bridge girders, pressure vessels |
| 20 | 3/4" | 20.10 | 20.50 | Heavy industry, shipbuilding |
Common stock diameters with the corresponding drill range. Imperial sizes follow the 1/32" increment convention (dash number = 32nds). Metric from ISO 1051.
Frequently asked questions
What is the 3x rule for rivet diameter?
The minimum rivet shank diameter should be at least three times the thickness of the thickest single plate in the joint. For example, if you are joining 2 mm aluminium sheet, the smallest acceptable rivet diameter is 6 mm. This rule ensures the rivet is stiff enough to transfer shear across the joint without the shank buckling or the surrounding material cracking around the hole.
How is rivet shank length calculated?
Shank length = total grip thickness + closing-head allowance. The closing-head allowance is a multiplier times the recommended rivet diameter: 1.5x for standard button heads (general use), 0.5x for countersunk heads, and 1.7-1.8x for pressurized or boiler applications. The raw result is then rounded up to the next standard increment (1/16" in imperial; 0.5 mm in metric) to match available stock.
What is grip length on a rivet?
Grip length is the total combined thickness of all materials being clamped together, measured through the hole. It is the distance the rivet shank must span before the closing head forms on the back side. Select a rivet whose grip range includes your total clamping thickness: too short and the rivet cannot clench; too long and the shop head will be malformed and weak.
How do I choose the right hole diameter for a rivet?
The hole diameter should be slightly larger than the rivet shank, typically by 0.1 mm to 0.25 mm (0.004" to 0.010" in imperial). This small clearance lets the rivet slide in without damaging the hole wall, while still producing a tight clamp after the shop head is formed. For aviation work, use the tighter end of this range and always cross-check against the specific rivet and alloy table in the aircraft SRM.
What is the minimum edge distance for rivets?
Minimum edge distance, the distance from the rivet centreline to any free edge of the plate, is at least 2x the rivet diameter for aluminium, 2.5x for steel, and 3x for composite structures. This prevents the plate from tearing through the edge under shear or tension loads. Many structural codes call for 2.5-3x as a preferred value even in aluminium, to provide a safety margin beyond the absolute minimum.
What is rivet pitch and how is it set?
Rivet pitch is the centre-to-centre distance between consecutive rivets in a row. The minimum is 4x the rivet diameter for aluminium, 4.5x for steel, and 5x for composites. The maximum pitch in aviation airframes is 6x the diameter to prevent inter-rivet buckling of the skin panel. For general structural joints, the upper limit is often set by load distribution requirements from an engineering calculation rather than a hard rule.
Do aviation rivets follow the same sizing rules?
Yes, with stricter tolerances. FAA AC 43.13-1B specifies a closing-head protrusion of 1.5x the rivet diameter, edge distance of 2x, and pitch between 4x and 6x the diameter. Hole tolerances are tighter than general construction (typically +0.002" to +0.004" over the shank). Aviation rivets also follow a dash-number naming convention: the first dash number is the diameter in 32nds of an inch and the second is the length in 16ths of an inch. Always verify against the specific aircraft SRM for the alloy, temper, and head style required.