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Wire Size Estimate Calculator
Estimate conductor area from voltage drop only. This is not final cable selection.
Preliminary voltage-drop estimate only. Not final cable selection. Ampacity, protection, installation method, temperature, insulation, local code and safety must be verified by a qualified professional.
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Formula
allowed_voltage_drop_v = voltage * max_drop required_area = coefficient * ρ * length * current / allowed_voltage_drop_v recommended_standard_size = first standard size >= required_area
Assumptions
- Inputs are user-provided.
- Results are preliminary estimates.
- Estimate is based only on voltage drop with PF fixed at 1.
Limitations
- Does not check ampacity, protection, installation method, temperature, insulation, local codes, or safety.
- AC reactance and low power factor are not modeled in this simplified estimate.
Sources / methodology
Solves the simplified voltage-drop equation for conductor area and rounds up to a standard metric size.
- Formula version
- 1.0.7
- Formula review date
- 2026-06-20
Source links
- NFPA NEC 2025 public input response PDF
- NFPA NEC 2020 first draft report PDF
- Schneider Electric - Determination of voltage drop
- Schneider Electric - Calculation of voltage drop in steady load conditions
- Schneider Electric - Maximum voltage drop limit
- Schneider Electric - Sizing and protection of conductors
- Schneider Electric - General method for cable sizing
- Copper Development Association - Copper building wire practices
- Cerrowire - Voltage Drop Calculator
- Southwire - Voltage Drop Calculator
Quick answer: Wire Size Estimate Calculator estimates allowed voltage drop from transparent input parameters and a visible formula. Results are informational estimates only and should be checked against the stated assumptions and limitations. This page is not a compliance document, installation approval, or final engineering design.
Input parameters
- System type: Single-phase AC
- Voltage (V): 230 V
- Current (A): 10 A
- One-way length (m): 20 m
- Conductor material: Copper
- Wire standard: Metric (mm²)
- Max voltage drop (%): 3 %
Output values
- Allowed voltage drop (V)
- Required area (mm²)
- Nearest standard size (mm²)
- Ampacity check required
Step-by-step example
Calculation for the example inputs shown above:
- ΔU = 230 × 3/100 = 6.9 V
- A = 1.014493 mm²
- Rounded up to available standard size: 1.5 mm²
This is a voltage-drop calculation, not final cable selection. Ampacity and protection must be checked independently.
Worked examples
Worked example with the form defaults
Example inputs: System type: Single-phase AC; Voltage: 230 V; Current: 10 A; One-way length: 20 m; Conductor material: Copper; Wire standard: Metric (mm²); Max voltage drop: 3 %. ΔU = 230 × 3/100 = 6.9 V. A = 1.014493 mm². Rounded up to available standard size: 1.5 mm². This is a voltage-drop calculation, not final cable selection. Ampacity and protection must be checked independently.
Alternative calculation scenario
Example inputs: System type: Single-phase AC; Voltage: 230 V; Current: 10 A; One-way length: 50 m; Conductor material: Copper; Wire standard: Metric (mm²); Max voltage drop: 3 %. ΔU = 230 × 3/100 = 6.9 V. A = 2.536232 mm². Rounded up to available standard size: 4 mm². This is a voltage-drop calculation, not final cable selection. Ampacity and protection must be checked independently.
What the result does not establish
A size that meets the voltage-drop target can still overheat or fail protection requirements. Check current capacity, installation method, grouping, insulation temperature and protective-device coordination separately.
Common mistakes
- Keep all units consistent with the field labels.
- Check whether the input values are measured, nameplate values or planning assumptions.
- Review the stated assumptions and limitations before using the estimate.
- A qualified professional must verify risk-sensitive real-world decisions.
What to check next
Check the inputs, limitations, sources and related calculators before using the estimate in a real decision.
FAQ
What does Wire Size Estimate Calculator calculate?
Wire Size Estimate Calculator estimates allowed voltage drop from transparent input parameters and a visible formula. Results are informational estimates only and should be checked against the stated assumptions and limitations. This page is not a compliance document, installation approval, or final engineering design.
What formula does this calculator use?
The visible formula starts with: allowed_voltage_drop_v = voltage * max_drop. The full formula, assumptions and limitations are shown on the page.
Can I use this as final electrical design?
No. The result is a preliminary estimate only and must be verified by a qualified professional and local rules.
Related calculators
This calculator provides an estimate for informational purposes only. It is not a certified engineering design, electrical safety approval, or professional installation recommendation. Always verify final decisions with a qualified professional and applicable local codes.