Wire Size Calculator
Calculate minimum conductor area and recommended AWG based on a DC voltage-drop limit, cable length, load current, supply voltage, and conductor material. Results are voltage-drop sizing estimates only and do not verify ampacity or electrical-code compliance.
Engineering tool
Wire Size Calculator
Find the minimum conductor area and smallest qualifying AWG based only on an entered DC voltage-drop limit. This is not an ampacity or code-compliance calculator.
Used as the percentage denominator and for estimated load voltage.
Sizing requires current greater than zero.
Physical source-to-load distance. The two-conductor DC loop uses twice this length.
Percentage is based on supply voltage: Vdrop / Vsupply × 100%.
Material presets reuse the WIR-001/WIR-002 shared AWG reference data.
Result console
- Minimum Area Based on Voltage-Drop Limit
- 5.74667mm²
- Recommended AWG Based on Voltage-Drop Limit
- AWG 9
- Predicted Voltage Drop
- 0.51973V
- Predicted Voltage Drop Percentage
- 4.3311%
- Recommended AWG Actual Area
- 6.63419mm²
- Predicted Loop Resistance
- 0.05197Ω
- Estimated Load Voltage
- 11.48027V
- Wire Power Loss
- 5.19732W
- Maximum Allowed Drop
- 0.6V
- Allowed Drop Percentage
- 5%
- One-Way Cable Length
- 10m
- Total Conductor Length
- 20m
- Load Current
- 10A
- Material
- Copper
- Resistivity
- 1.724e-8Ω·m
Minimum size is based on the specified voltage-drop limit only. Ampacity, code compliance, insulation rating, installation method, bundling, termination rating, and fault protection are not verified.
Formula reference
Voltage-drop wire sizing formulas
WIR-003 solves the inverse voltage-drop problem and then verifies the selected AWG with the forward WIR-002 voltage-drop model.
Rloop = 2ρL/AVdrop = I × RloopArequired = 2ρLI / Vdrop,maxVdrop,max = Vsupply × p/100%drop = Vdrop/Vsupply × 100%Variable definitions
- ρ
- conductor resistivity
- L
- one-way cable length
- I
- load current
- A
- conductor cross-sectional area
- p
- maximum voltage-drop percentage
WIR-003 Formula Audit
| Core Sizing Formula | Arequired = 2ρLI / Vdrop,max. |
|---|---|
| One-Way Length Convention | L is source-to-load one-way cable length. |
| Total Conductor Length Convention | Ltotal = 2 × Lone-way for two equal DC conductors. |
| Percentage Drop Formula | %drop = Vdrop / Vsupply × 100%. |
| Allowed Drop Conversion | Vdrop,max = Vsupply × p / 100 in percentage mode. |
| Required Area Formula | Arequired uses the complete two-conductor loop relation Rloop = 2ρL/A. |
| AWG Selection Rule | Select the smallest conductor whose raw AWG area is greater than or equal to required area. |
| AWG Direction | Larger AWG number means smaller conductor area. |
| AWG Precision Policy | Selection uses raw shared dataset values, not rounded display values. |
| Post-Selection Verification | Selected AWG is forward-calculated with WIR-002 to verify voltage drop. |
| AWG Out-of-Range Handling | No AWG is returned if the required area exceeds the supported dataset. |
| Material Data Reuse | Copper/aluminum presets reuse WIR-001 material data. |
| Reference Temperature Policy | Preset resistivity values are approximate reference values near 20°C. |
| Temperature Boundary | No full conductor temperature correction. |
| DC / AC Boundary | DC and low-frequency resistive sizing only. |
| Three-Phase Boundary | No partial √3 three-phase shortcut. |
| Ampacity Boundary | No current capacity, fuse, breaker, or thermal approval. |
| Code Compliance Boundary | No NEC, IEC, UL, CSA, or local-code compliance result. |
| WIR-002 Boundary | WIR-002 forward-calculates voltage drop for known wire. |
| WIR-004 Boundary | WIR-004 will solve maximum cable length; WIR-003 does not. |
Worked Examples
| Case | Calculation | Result |
|---|---|---|
| Critical area | 2 × 1.724e-8 × 10m × 10A / 0.5V | 6.896mm² |
| 12V at 5% | Vdrop,max=0.6V | 5.74667mm² |
| 24V at 5% | Vdrop,max=1.2V | 2.87333mm² |
| Percentage conversion | 12V × 5 / 100 | 0.6V |
| Exact round trip | Arequired into WIR-002 | recovers allowed drop |
| AWG selection | raw AWG area ≥ required area | smallest qualifying conductor |
| Next thinner check | next smaller area | fails requirement when present |
| Total length | one-way 10m | 20m conductor path |
| Double current | I ×2 | Arequired ×2 |
| Double length | L ×2 | Arequired ×2 |
| Double resistivity | ρ ×2 | Arequired ×2 |
| Double drop limit | Vdrop,max ×2 | Arequired ÷2 |
| Higher supply at same % | 24V vs 12V | smaller required area |
| Higher percentage | 10% vs 5% | smaller required area |
| Copper vs aluminum | same geometry | aluminum requires more area |
| mV conversion | 1mV | 0.001V |
| mA conversion | 1mA | 0.001A |
| ft conversion | 1ft | 0.3048m |
| in conversion | 1in | 0.0254m |
| mm² conversion | 1mm² | 1e-6m² |
| Ω·mm²/m conversion | 1Ω·mm²/m | 1e-6Ωm |
| µΩ·cm conversion | 1µΩ·cm | 1e-8Ωm |
| Zero current | I=0 | rejected for sizing |
| Zero length | L=0 | rejected for sizing |
| Out of range | required area beyond AWG table | exact area retained, no undersized AWG |
Engineering Notes
- WIR-003 sizes conductors from a voltage-drop requirement only.
- The primary result is minimum conductor area, not a universal safe wire size.
- Recommended AWG is selected from raw shared AWG area data.
- AWG numbers run backward: smaller numbers are larger conductors.
- One-way length is doubled internally for the two-conductor DC loop.
- Copper and aluminum resistivity values come from shared material data.
- Reference resistivity is not the same as hot conductor resistance.
- Allowed voltage-drop percentage is based on supply voltage.
- Higher current or longer cable requires larger conductor area.
- Higher supply voltage allows more absolute drop for the same percentage limit.
- The calculator does not check ampacity, breaker size, fuse size, or code compliance.
- Insulation rating, ambient temperature, bundling, and installation method still matter.
- Termination ratings and fault protection must be checked separately.
- Complete AC or three-phase cable sizing is outside WIR-003.
Common Mistakes
- Treating the result as ampacity approval.
- Forgetting the return conductor.
- Entering total loop length as one-way length.
- Doubling length twice.
- Entering 5% as 0.05 when the field expects percent.
- Using load voltage as the percentage denominator.
- Selecting an AWG smaller than the required area.
- Misunderstanding AWG number direction.
- Using rounded AWG area instead of raw data.
- Using cable outside diameter as conductor area.
- Assuming copper and aluminum have the same resistivity.
- Ignoring conductor temperature.
- Using DC sizing as a complete AC cable design.
- Assuming 3% or 5% is universal for every system.
Support reference
FAQ
How do I calculate required wire size?
For a two-conductor DC cable, use Arequired = 2ρLI / Vdrop,max, where L is one-way cable length, I is load current, ρ is resistivity, and Vdrop,max is the allowed voltage drop.
How do I size wire for voltage drop?
Choose the maximum allowed voltage drop, calculate the minimum conductor area, then select the smallest available AWG conductor whose raw area is greater than or equal to that requirement.
What is the wire size formula?
The voltage-drop sizing formula is Arequired = 2ρLI / Vdrop,max for a two-wire DC loop using one-way source-to-load cable length.
How do I calculate required conductor area?
Convert all inputs to SI units, calculate the maximum allowed voltage drop, then divide 2ρLI by that drop limit.
How do I choose AWG from required area?
Compare the calculated required area against the shared AWG dataset and choose the smallest conductor whose raw area is not smaller than the requirement.
Does a larger AWG number mean a larger wire?
No. AWG is reversed: larger gauge numbers usually mean smaller conductor area and higher resistance.
Why is cable length doubled?
Current flows through the outgoing conductor and returns through another conductor, so the total conductor length is twice the one-way physical cable run.
What does one-way cable length mean?
One-way cable length is the physical distance from source to load. The calculator reports total conductor length separately.
How does current affect required wire size?
Required conductor area is directly proportional to current. Doubling current doubles the required area for the same drop limit.
How does cable length affect required wire size?
Required conductor area is directly proportional to one-way cable length. Longer cable runs need more conductor area for the same voltage-drop limit.
How does supply voltage affect wire size?
In percentage mode, higher supply voltage allows a larger absolute drop for the same percentage limit, so required area decreases.
How does allowed voltage drop affect wire size?
Required area is inversely proportional to the allowed voltage drop. A stricter drop limit requires a larger conductor.
How do I size wire using a percentage voltage drop?
The calculator converts the percentage to voltage using Vdrop,max = Vsupply × percentage / 100, then applies the conductor sizing formula.
Is voltage drop percentage based on supply voltage?
Yes. It is based on supply voltage, matching WIR-002: %drop = Vdrop / Vsupply × 100%.
Can I size copper wire?
Yes. Copper is available from the shared AWG material dataset and is the default material preset.
Can I size aluminum wire?
Yes. Aluminum is available as a shared material preset and generally requires more area than copper for the same drop limit.
Does wire temperature affect the result?
Yes. Conductor resistance changes with temperature. This calculator uses reference resistivity and does not perform full temperature correction.
Does this calculator account for conductor temperature?
No. Full conductor temperature correction belongs to WIR-011. Use margin or measured hot resistance for critical wiring.
Does this calculator check ampacity?
No. It only checks the entered voltage-drop criterion and does not verify thermal current capacity.
Is the recommended AWG NEC compliant?
No NEC compliance is implied. The recommendation is only based on the entered voltage-drop limit and shared AWG area data.
Is the recommended AWG IEC compliant?
No IEC compliance is implied. Verify final conductor selection against applicable standards and installation requirements.
Is 3% voltage drop always required?
No. Acceptable voltage drop depends on the system, load tolerance, regulation budget, and applicable standards.
Can I use this calculator for AC circuits?
Only as a simple low-frequency resistive estimate. Complete AC sizing may need reactance, power factor, skin effect, and proximity effect.
Can I use this calculator for three-phase circuits?
No. WIR-003 does not provide a complete three-phase cable sizing model.
What happens if the required area is larger than the supported AWG range?
The calculator keeps the exact required area and shows an out-of-range warning instead of returning an undersized AWG.
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