SWG to Diameter and Area Calculator
Wire diameter and cross-section from a Standard Wire Gauge (SWG) number. With the formula, a worked example and typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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About this calculator
This page calculates diameter, diameter and cross-section from SWG number. Change any value or its unit and the result updates. The steps below show the working for the default values, so you can check each line against your own method.
Limits of this calculator
SWG and AWG differ: SWG 18 is 1.219 mm, AWG 18 is 1.024 mm. Always state which gauge system a drawing or order uses.
Cross-check: 57 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review.
Verification status: Engineering reference
Engineering reference. Formula and method documented and tested against separately coded reference calculations. Not yet Verified: the evidence listed on this page is still needed.
What this calculator checks
- The arithmetic of the published formula for the values you entered, in the units shown.
What remains unverified
- That the inputs suit your application. Take ratings, resistances and constants from the manufacturer data sheet or project specification.
Verification register entry
| Calculation author | Rahul Sharma (author) |
|---|---|
| Technical review | No independent technical review has been carried out |
| Individual professional approval | Not recorded |
| Formula reference | not recorded |
| Standard and edition | Not applicable: SWG is a historical gauge table conversion, not a current universal cable-selection or ampacity method. Gauge conversion does not establish conductor compliance or current-carrying capacity. |
| Standard review state | Not applicable |
| Scope-screening note | not recorded |
| Cross-check test cases | 57 reference vectors (tests/reference_vectors.json) |
| Review date | not recorded |
| Next review date | not recorded |
| Status | Engineering reference |
Needed before this calculator can be marked Verified: reviewer name, qualification and review date; exact formula reference; formula source (textbook or standard); next review date.
Formula
Worked example
| Input | Value |
|---|---|
| SWG number (use 0 for 1/0, −1 for 2/0, down to −6 for 7/0) | 18 |
- SWG 18 = 0.048 in (table value)
- d = 0.048 × 25.4 = 1.2192 mm
- A = π d² / 4 = 1.1675 mm²
Assumptions
- Solid round conductor
- Diameters are the standard SWG table values; the series is a table, not a formula
SWG and AWG differ: SWG 18 is 1.219 mm, AWG 18 is 1.024 mm. Always state which gauge system a drawing or order uses.
Inputs and results
| Input | Unit | Allowed or shown | Note |
|---|---|---|---|
| SWG number (use 0 for 1/0, −1 for 2/0, down to −6 for 7/0) | (number) | -6 or more, up to 50 | SWG is not the same as AWG. The same number gives a different wire. |
| Result | Unit | Allowed or shown | Note |
|---|---|---|---|
| Diameter | mm | Shown to 3 decimal places | |
| Diameter (inches) | in | Shown to 4 decimal places | |
| Cross-section | mm² | Shown to 4 decimal places |
How it is calculated
Each input is converted to the base unit of its quantity, the formula above is applied in the order shown in the worked example, and each result is shown in the unit you choose. Results are held at full precision and rounded only for display, except where a step selects a standard size, as the worked example shows. A value outside its allowed range is refused with a message instead of giving a result.
How the result changes with swg number (use 0 for 1/0, −1 for 2/0, down to −6 for 7/0)
| SWG number (use 0 for 1/0, −1 for 2/0, down to −6 for 7/0) | Diameter (mm) | Diameter (in) | Cross-section (mm²) |
|---|---|---|---|
| 0 | 8.23 | 0.324 | 53.1921 |
| 6 | 4.877 | 0.192 | 18.6793 |
| 10 | 3.251 | 0.128 | 8.3019 |
| 14 | 2.032 | 0.08 | 3.2429 |
| 18 | 1.219 | 0.048 | 1.1675 |
| 24 | 0.559 | 0.022 | 0.2452 |
| 30 | 0.315 | 0.0124 | 0.0779 |
Other inputs are the same as in the worked example above.
Standards and further reading
- IEC 60364-5-52 (selection and erection of wiring systems, current-carrying capacity)
- IEC 60364-4-43 (protection against overcurrent, short-circuit withstand k factors)
- IEC 60228 (conductor sizes)
- IEC 60287 (calculation of cable current rating)
Ampacity and grouping factors come from your cable data sheet or your licensed copy of the standard; see STANDARDS.md for the method constants Elecmetric does use. These are named as background reading. Elecmetric does not embed clause text or rating tables, and the reviewer record for this calculator is separate from this list.
Frequently asked questions
What do I need to enter?
Enter sWG number (use 0 for 1/0, −1 for 2/0 and down to −6 for 7/0). Change the unit of a value with its selector and the result stays the same.
What does this calculator assume?
Solid round conductor. Diameters are the standard SWG table values; the series is a table, not a formula.
Which calculators should I use next?
Common next steps are AWG to Diameter and Area and Voltage Drop from Conductor Size. The related links at the bottom of this page open them.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. 57 reference cases, calculated from textbook formulas coded separately from the engine by the same author, agree with this calculator. This is not an independent review. Check design values against the standard and the equipment data you work to.
Formula guides and reference
Longer explanations with worked examples and tables, written for the same topic.
- AWG and SWG Wire Gauge Converter: gauge numbers, diameters and areas
- Conductor Resistance Formulas and Temperature: Conductor resistance formulas: resistance from length, area and resistivity, correction for temperature
More Cable Engineering calculatorsAll engineering calculatorsSWG to Diameter and Area in Elecmetric