Reference chartLow code sensitivityLast reviewed April 29, 2026
Electrical reference chart
Wire Gauge Diameter Chart
Use this reference for nominal bare conductor diameter, then switch to manufacturer outside-diameter data when the task is physical installation fit.
Quick reference table
Wire gauge diameter is a bare-metal geometry reference. It is useful for identification, drawing review, and AWG math, but it is not the diameter to use for conduit fill, tray fill, cable glands, or terminal fit. Physical installation work needs the finished insulated conductor or cable outside diameter from the product data.
Nominal bare AWG conductor diameters
| AWG | Diameter inches | Diameter mm | Field use |
|---|---|---|---|
| 18 AWG | 0.0403 | 1.02 | Small control conductors |
| 16 AWG | 0.0508 | 1.29 | Control or fixture lead reference |
| 14 AWG | 0.0641 | 1.63 | Small branch-circuit geometry |
| 12 AWG | 0.0808 | 2.05 | Common branch-circuit geometry |
| 10 AWG | 0.1019 | 2.59 | Equipment lead geometry |
| 8 AWG | 0.1285 | 3.26 | Larger conductor cross-check |
Which diameter belongs in the next task
| Task | Use this dimension | Do not use |
|---|---|---|
| Gauge identification | Bare conductor diameter or area | Insulation outside diameter alone |
| Conduit fill | Insulated conductor or cable outside diameter | Bare AWG diameter |
| Cable tray planning | Finished cable outside diameter or width | Conductor metal diameter |
| Terminal or lug fit | Manufacturer conductor range and class | A chart diameter without lug data |
Formula basis
Diameter in inches = 0.005 x 92^((36 - AWG) / 39).
- AWG is the gauge number.
- Diameter is nominal bare conductor diameter before insulation or jacket construction.
Worked examples
Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.
- The chart lists nominal bare conductor diameter and rounds metric values for reference.
- Solid, stranded, compact, insulated, and jacketed constructions can have different finished dimensions.
- Manufacturer datasheets control physical fit decisions when finished cable or insulated conductor size matters.
Code and standard notes. Planning limits that should be checked before final equipment selection.
- For conduit, raceway, tray, or enclosure fill, use listed conductor or cable dimensions and the applicable calculator path rather than bare AWG diameter alone.
How to use this chart
Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.
- Identify the physical questionWrite whether the diameter is being used for identification, drawing review, conduit planning, cable tray spacing, or termination review.
- Attach product data when neededFor installation decisions, attach the cable or conductor datasheet that shows actual outside diameter and construction.
- Keep area and diameter separateUse area values for current and voltage-drop work, and use finished outside diameter for physical fit work.
Common mistakes to avoid. Review these before turning chart current into an equipment decision.
- Using bare conductor diameter for conduit fill when the insulated outside diameter is the value that matters.
- Assuming solid and stranded conductors have the same finished outside diameter after insulation and jacket construction are included.
- Using a diameter chart to approve a lug or terminal without checking the listed conductor range and conductor class.
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.
Can this chart be used for conduit fill?
No. Conduit fill depends on the outside diameter or area of insulated conductors or cables, not only the bare conductor diameter.
Why do two 12 AWG products have different finished diameters?
AWG describes conductor metal size. Insulation thickness, stranding, jacket, compact construction, and cable assembly design change finished diameter.
What should I use for lug fit?
Use the lug or terminal listing, conductor material, conductor class, and manufacturer range. A bare-diameter chart is not enough for termination approval.