Bonsai Wire Gauge Calculator
Enter branch diameter to find the wire thickness to reach for before you bend it.
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Common Branch Diameter — Wire Size Pairs
| Branch Diameter | Copper Wire | Aluminum Wire |
|---|---|---|
| 2mm | 1.0mm (18 AWG) | 1.0mm |
| 3mm | 1.0mm (18 AWG) | 1.0–1.5mm |
| 5mm | 1.2–1.5mm (17–15 AWG) | 1.5–2.5mm |
| 8mm | 2.0–2.5mm (12–10 AWG) | 2.5–4.0mm |
| 10mm | 2.5–3.0mm (10–9 AWG) | 3.0–5.0mm |
| 15mm | 4.0–5.0mm (6–4 AWG) | 5.0–6.0mm |
How to Pick Bonsai Wire Gauge by Branch Diameter
The commonly-taught bonsai-wiring guideline sizes wire relative to the branch it will hold: copper wire at roughly 1/4 to 1/3 of the branch's diameter, anodized aluminum at roughly 1/3 to 1/2. Copper is stiffer for its thickness and work-hardens as it's bent, so it holds a given branch at a thinner gauge than aluminum needs for the same job.
Formula: copper diameter = branch diameter × 0.25 to 0.33. Aluminum diameter = branch diameter × 0.33 to 0.5. A 10mm branch: copper 2.5–3.3mm, aluminum 3.3–5.0mm. Round to the nearest size your supplier stocks — most bonsai wire comes in 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 6.0mm diameters (copper is also commonly labeled by AWG: roughly 18 AWG at 1.0mm down to 4 AWG at 5.0mm).
This ratio is a starting point, not a guarantee. Wood hardness varies by species — junipers and pines hold wire more readily than soft-wooded deciduous branches of the same diameter — and a branch's own taper, health, and flexibility change how much holding power it actually needs. Sizing one gauge up is reasonable for a branch you plan to bend aggressively; sizing down risks the wire slipping before the branch sets, which usually means re-wiring the same branch a second time.
Wire longevity matters as much as gauge: aluminum should come off in a few months as the branch thickens, while copper can stay on longer since it work-hardens and holds its set, but either left on too long will scar the bark as the branch grows into it. Check wired branches every few weeks during the growing season.
See also: Plant Spacing Calculator · Soil Volume Calculator