Wire Bundle Diameter: Circle Packing and the Glenair Method

Why bundle diameter is a real design number

Bundle a harness of wires together and the finished diameter drives a surprising amount of the design: the size of the conduit or grommet it passes through, the clamp and routing spacing, how much it weighs, and whether it fits the space claim in a packed engine bay or airframe. But wires don't pack into a neat circle — round shapes leave gaps — so estimating the bundle diameter takes a bit of geometry. There are two standard ways to do it.

Method 1: circle packing

The direct approach is to actually pack the circles: arrange the individual wire cross-sections as tightly as possible and measure the smallest circle that encloses them. This captures the real geometry — a bundle of mixed-gauge wires nests differently than uniform ones — and it's what drives a cross-section diagram. The catch is that optimal circle packing is a hard problem; practical tools use a heuristic (greedy tangent placement), which is close but not provably the tightest possible arrangement.

Method 2: the Glenair multiplication-factor table

Industry's pragmatic shortcut is the published Glenair Wire Bundle Diameter method: take the arithmetic-mean wire diameter and multiply by a factor that depends on the number of wires. It's a statistical fit — a single number that captures how bundles of N wires typically come out, without modelling the exact packing. It's fast, it's the recognised industry cross-check, and it's why a good estimate reports both the packed and the Glenair-factor result: if they agree, you can trust the number.

Coverings add to the outside

The bare bundle is only the start. Overbraid, heat-shrink, and sleeving each add wall thickness around the outside, growing the finished OD. A covering's finished diameter assumes it wraps snugly against the bundle — a first-order estimate, since real tubing recovers to its own limits and loose coverings sit larger.