The calculator
Runs in your browser. Inches or millimetres at the top. Leave the last field blank unless you are checking a hole that already exists.
How the rule works
Edge distance is expressed as a multiple of D, the rivet's shank diameter — not the head diameter, and not the drilled hole. A 1/8" rivet has D = 0.125", so its minimum edge distance is 0.250".
Minimum, protruding head: 2D. Below this the sheet between the hole and the free edge does not have enough material to carry the bearing load, and the failure mode is a tear-out — the rivet simply pulls a channel through to the edge.
Minimum, countersunk head: 2.5D. Countersinking removes material from the top of the sheet around the hole, so the effective section is thinner. The extra half-diameter compensates.
Preferred: 2.5D. The figure the FAA Airframe Handbook recommends, and the number to design to. The half-diameter above the minimum is your working margin for drill wander, a hole opened up on removal, and edge dressing after trimming.
Maximum: 4D. Rarely the one people get wrong, and rarely the one people know. Past 4D the strip of material between the fastener line and the free edge is unsupported over too long a span; under compression it buckles and lifts, and the joint stops behaving like a joint.
Note that for countersunk rivets the minimum and the preferred figure coincide at 2.5D. Treat 2.5D as a floor there, not a target — aim above it where the drawing gives you room.
Worked example
A row of AN470AD4 universal-head rivets — 1/8" shank — along a trimmed skin edge.
- D = 0.125".
- Minimum edge distance = 2 × 0.125 = 0.250".
- Preferred edge distance = 2.5 × 0.125 = 0.313".
- Maximum edge distance = 4 × 0.125 = 0.500".
- You scribe your rivet line at 0.313" from the trimmed edge. A hole that wanders 0.05" toward the edge lands at 0.263" — still legal. Had you scribed at the 0.250" minimum, the same wander would have put it out of limits.
Line at 0.313" (5/16"). That is why you lay out to the preferred figure and not to the minimum.
Limits — when NOT to use this
This calculator applies the general rule for solid aluminum rivets in sheet metal. That rule is a floor for general practice, not authority for a specific repair.
- Approved data always wins. If the SRM, the AMM, the type certificate holder's repair drawing or an approved 8110-3 specifies an edge distance, that figure governs — even where it is more restrictive than this one, and especially where it is.
- Blind and special fasteners have their own limits. CherryMAX, Hi-Lok, Jo-Bolt and lockbolt families are governed by the manufacturer's installation data, not by the solid-rivet rule. Some require more than 2D.
- Not for composites. Fastener edge distance in composite laminates is a different problem governed by ply layup and bearing/bypass interaction. Do not carry these numbers across.
- Countersunk into thin sheet. If the countersink breaks through — a knife edge — edge distance is no longer your controlling problem. Dimple instead of machine countersink below the thickness limit for the rivet size.
- Edge distance is one of three checks, not the check. Rivet pitch, transverse pitch and edge distance are evaluated together. A layout can pass all three and still be the wrong repair.
- Measure to the finished edge. If the part will still be trimmed, dressed or radiused, the edge you are measuring to is not the edge that will exist.
Questions people actually ask
Is edge distance measured from the center of the hole or the edge of the hole?
From the center. This is the single most common error and it makes a hole look compliant when it is not — measuring from the hole edge understates the distance by half a diameter, so a hole you read as 2D is really 1.5D.
Does edge distance change with sheet thickness?
No. The 2D / 2.5D / 4D rule is a function of rivet diameter only. Sheet thickness drives other decisions — rivet diameter selection, dimple versus machine countersink, maximum pitch — but not edge distance.
What is the minimum edge distance for a countersunk rivet?
2.5D, against 2D for a protruding head. The countersink removes material from the upper surface, thinning the effective section around the hole, and the extra half-diameter compensates.
Can edge distance be too large?
Yes, and it is the half of the rule most people have never heard. Past 4D the unsupported strip between the fastener line and the free edge buckles under compression. Skin flutter and oil-canning along an over-set edge are the visible symptom.
My hole came out at 1.9D. Can I just fit a larger rivet?
Going up a rivet size increases D, so the required edge distance goes up as well — the ratio gets worse, not better. Oversizing to the next rivet diameter is a legitimate repair technique for an enlarged or damaged hole, but it does not fix an edge distance problem, and which remedy applies is a repair-design decision against approved data.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 4, ¶4-57 and Figure 4-5 — the 2D minimum edge distance and 3D minimum pitch for single-row rivets, verbatim; row minimums for double and triple rows in Figure 4-5. Note that the AC does not state a maximum edge distance, a countersunk minimum, or a transverse-pitch percentage — those come from the handbook below.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 4 — “It should not be less than 2 or more than 4 rivet diameters and the recommended edge distance is about 2½ rivet diameters… the minimum edge distance for countersunk rivets is 2½ times the diameter of the rivet.” Also the source for transverse pitch at 75% of pitch with a 2½ D floor, and for rivet length = grip + 1.5D.
- FAA-H-8083-31, Aviation Maintenance Technician Handbook — Airframe — rivet layout terminology and the definition of edge distance from hole center.
Rivet layout card, printable
Edge distance, pitch and transverse pitch for all five common rivet sizes on one page — worked out in inches and mm so you are not doing arithmetic on a scrap of aluminum.