# Wire size calculator

> Free conservative AC/DC cable cross-section calculator at https://wiresize.app/. Enter voltage, current, and one-way length. The result is the larger of voltage-drop size and heating (ampacity) size, on the IEC 60228 series, plus a nearest-AWG area match. It is a progressive web app: it can be installed locally on PCs as well as iOS and Android, and the calculator works offline.

Not a wiring design and not a substitute for an electrician or national rules (IEC 60364 / local codes). It does not check short-circuit rating, earth-fault loop impedance, or mechanical protection.

Default example (in the HTML without JavaScript): 12 V DC, 5 A, 5 m one-way, copper, 3% drop → 4 mm² (≈ 11 AWG). Voltage drop governs; heating alone would allow 0.75 mm². S_min ≈ 3.08 mm². For marine 12 V runs, use tin-coated (tinned) copper to resist corrosion; the calculated mm² is the same as bare copper.

- Standard sizes: IEC 60228 (0.75–240 mm²).
- AWG equivalent: nearest ASTM B258 conductor area (then kcmil above 4/0). 4 mm² → 11 AWG (4.17 mm²), not 12 AWG (3.31 mm²). This is an area match, not an NEC ampacity size.
- Resistivity at 70 °C PVC (CLC/TR 50480): copper 22.2 mΩ·mm²/m; aluminium 35.3 mΩ·mm²/m.
- DC / 1-phase: go and return, ΔU = 2·I·L·(R cos φ + X sin φ). DC uses cos φ = 1 and X = 0, so S = 2·ρ·L·I / ΔU_max. L is one-way metres.
- 3-phase balanced: ΔU = √3·I·L·(R cos φ + X sin φ), X ≈ 0.08 Ω/km.
- DC ampacity: ISO 10133 (ELV, single conductor, 30 °C, 70 °C). Drop limits 3% typical, 10% optional.
- AC ampacity: conservative in-conduit Method B, 30 °C, PVC 70 °C. Drop guidance 3% lighting / 5% other.

## Pages

- [Wire size calculator](https://wiresize.app/): Interactive AC/DC calculator. Canonical human page. Installable on PC, iOS, and Android; works offline.
- [FAQ](https://wiresize.app/#faq): Plain-language cable-size questions. Labeled FAQ. First question: which size cable should I use? Worked examples: 12 V DC 5 A 5 m → 4 mm² (11 AWG); 12 V 5 A 10 m → 10 mm²; 24 V same load → 2.5 mm²; 4 mm² → 11 AWG not 12 AWG; 230 V 16 A 10 m → 1.5 mm². Marine: use tin-coated (tinned) copper against corrosion; calculated mm² matches bare copper.
- [Method](https://wiresize.app/#method): Same formulas as above, on the page.

## Optional

- [Sitemap](https://wiresize.app/sitemap.xml)
- [robots.txt](https://wiresize.app/robots.txt)