Electronics
Wire Gauge & Voltage Drop Calculator
Give it your load current, one-way wire length, supply voltage, and an acceptable voltage drop, and it'll calculate drop across common AWG sizes and flag the smallest gauge that stays within your target.
Estimate voltage drop across common AWG sizes and find the smallest gauge that stays under your target drop.
| Gauge | Drop (V) | Drop (%) |
|---|---|---|
| 18 AWG | 5.599 | 4.67% |
| 16 AWG | 3.522 | 2.93% |
| 14 AWG | 2.215 | 1.85% |
| 12 AWG | 1.393 | 1.16% |
| 10 AWG | 0.876 | 0.73% |
| 8 AWG | 0.551 | 0.46% |
| 6 AWG | 0.346 | 0.29% |
| 4 AWG | 0.218 | 0.18% |
| 2 AWG | 0.137 | 0.11% |
| 1 AWG | 0.109 | 0.09% |
| 1/0 AWG | 0.086 | 0.07% |
| 2/0 AWG | 0.068 | 0.06% |
| 3/0 AWG | 0.054 | 0.05% |
| 4/0 AWG | 0.043 | 0.04% |
Voltage drop from wire resistance
V_drop = I × (2 × L × ρ / A)
Resistance depends on the conductor's resistivity (ρ), the round-trip length (2×L, since current travels out and back), and the cross-sectional area (A) implied by the AWG size. Multiplying that resistance by current gives the voltage drop.
How to use
- Measure the one-way distance from the source to the load — the calculator accounts for the return path automatically.
- Enter the load's expected current draw and your target maximum drop (3% is a common guideline for branch circuits, 5% for feeders).
- Compare the table of gauges and drops; pick the recommended gauge or size up if the run may see more current later.
Example
Input: 15A load, 30 ft one-way, 120V supply, 3% max drop
Output: Recommended: 16 AWG copper (~2.9% drop)
Student-friendly breakdown
This walkthrough emphasizes the most searched ideas for Wire Gauge & Voltage Drop Calculator: wire gauge calculator, voltage drop calculator, awg calculator, wire size calculator for amps. Start with the formula above, then follow the guided steps to double-check your work. For quick revision, highlight the givens, plug into the equation, and finish by verifying your units.
Need more support? Use the links below to open the long-form guide, browse additional examples, or hop into adjacent calculators within the same topic — each one is a quick way to double-check your work or handle a related question without starting from scratch.
Deep dive & study plan
Wire Gauge & Voltage Drop Calculator: Estimates voltage drop across AWG wire sizes and recommends a gauge for your run. It's built around wire gauge calculator, awg voltage drop, wire size calculator, so you can go from a raw question to a checked answer without switching tools.
The math behind it: Resistance depends on the conductor's resistivity (ρ), the round-trip length (2×L, since current travels out and back), and the cross-sectional area (A) implied by the AWG size. Multiplying that resistance by current gives the voltage drop. The core relationship is V_drop = I × (2 × L × ρ / A), shown above the calculator so you can see exactly how your inputs turn into the result.
To use it well: (1) Measure the one-way distance from the source to the load — the calculator accounts for the return path automatically. (2) Enter the load's expected current draw and your target maximum drop (3% is a common guideline for branch circuits, 5% for feeders). (3) Compare the table of gauges and drops; pick the recommended gauge or size up if the run may see more current later. Keep your units consistent as you go, and re-run a case you already know the answer to — it's the fastest way to catch a typo before it throws off a result you're relying on.
Worked example: entering 15A load, 30 ft one-way, 120V supply, 3% max drop returns Recommended: 16 AWG copper (~2.9% drop). Try swapping in your own numbers next, especially a case you're unsure about, before you use this for something that matters.
Quick retention checklist
- Speak the formula aloud (or annotate it) so the relationships stick.
- Write each step in your own words and compare with the numbered list above.
- Swap in new numbers for the Example to make sure the calculator (and your logic) handles edge cases.
- Check at least one related calculator below — it's the fastest way to confirm your numbers still line up from a different angle.
FAQ & notes
Does this replace an electrician or the NEC ampacity tables?
No. This estimates voltage drop from wire resistance for planning purposes. Building wiring must also meet ampacity, insulation, and code requirements — check the NEC tables or a licensed electrician for anything permanent or safety-critical.
Why does aluminum need a bigger gauge than copper for the same job?
Aluminum has roughly 1.6× the resistivity of copper, so it needs a larger cross-sectional area (a lower AWG number) to carry the same current with the same voltage drop.
What formula does the Wire Gauge & Voltage Drop Calculator use?
Resistance depends on the conductor's resistivity (ρ), the round-trip length (2×L, since current travels out and back), and the cross-sectional area (A) implied by the AWG size. Multiplying that resistance by current gives the voltage drop.
How do I use the Wire Gauge & Voltage Drop Calculator?
Measure the one-way distance from the source to the load — the calculator accounts for the return path automatically. Enter the load's expected current draw and your target maximum drop (3% is a common guideline for branch circuits, 5% for feeders). Compare the table of gauges and drops; pick the recommended gauge or size up if the run may see more current later.