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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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No account required. Calculation history is not stored.
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)
- Nearest standard size (AWG)
- Ampacity check required
Step-by-step example
- Enter values into the calculator fields.
- Run the calculation and review the result values.
- Compare the result with the assumptions, limitations and sources below.
Worked examples
Small load example
Use Wire Size Estimate Calculator with realistic household or workshop inputs first, then compare the estimate with a bill, label, nameplate, or manufacturer data.
Input sensitivity example
Change one major input at a time to see which variable drives the estimate most before you compare options or make a purchase decision.
Caution example
If the result affects wiring, protection, installation method, grounding, or cable selection, use it only as a preliminary estimate and verify with a qualified professional.
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.