2.9633 mm² is the example result. This is a copper cross-sectional voltage-drop estimate, not an AWG lookup or an ampacity selection. Installation, temperature and protective-device checks are separate.
This is a copper cross-sectional voltage-drop estimate, not an AWG lookup or an ampacity selection.
Distinguishing electrical arithmetic from equipment selection
This is a copper cross-sectional voltage-drop estimate, not an AWG lookup or an ampacity selection. Installation, temperature and protective-device checks are separate. Power, energy, voltage and current describe different quantities. Watts represent a rate; watt-hours represent energy over time. Battery and inverter losses can reduce usable runtime even when the rated capacity is unchanged.
What the model includes
Result = ((2 × [One-way copper circuit length (ft)] × .3048 × [Current (A)] × .0175) ÷ ([System voltage (V)] × [Maximum voltage drop (%)] ÷ 100)) Read unit labels before comparing results. Motor estimates depend on phase, efficiency and power factor; energy budgets depend on duration and duty cycle. Nameplate values and measured consumption may differ under real loads. Treat the output as the stated estimate. It does not select a code-compliant conductor, protective device or complete installation. Equipment specifications and applicable requirements remain part of the design decision.
Example with the supplied inputs
One-way copper circuit length (ft): 50; Current (A): 20; Maximum voltage drop (%): 3; System voltage (V): 120. Result: 2.9633 mm². The values are illustrative.
Compare one changed input
One-way copper circuit length (ft) changes from 50 to 55. The result becomes 3.2597 mm². All other inputs remain fixed.
Calculation rule
Result = ((2 × [One-way copper circuit length (ft)] × .3048 × [Current (A)] × .0175) ÷ ([System voltage (V)] × [Maximum voltage drop (%)] ÷ 100))
Inputs and output
| Input | Example value | Entry convention |
|---|---|---|
| One-way copper circuit length (ft) | 50 | Measure one-way copper circuit length (ft) in the displayed unit. Convert the source measurement before entry if it uses another system; a changed label does not perform a unit conversion. |
| Current (A) | 20 | Use the source quantity represented by current (a). Keep the counted population fixed and avoid mixing a unit value with a period total. |
| Maximum voltage drop (%) | 3 | Enter maximum voltage drop (%) on the percentage scale used in the formula (20 means 20%, not 0.20). Keep its base and reporting period consistent with the other inputs. |
| System voltage (V) | 120 | Use the source quantity represented by system voltage (v). Keep the counted population fixed and avoid mixing a unit value with a period total. |
Output: 2.9633 mm² is the example result. This is a copper cross-sectional voltage-drop estimate, not an AWG lookup or an ampacity selection. Installation, temperature and protective-device checks are separate. Unit: mm².
How to use the page
Collect the inputs
Gather One-way copper circuit length (ft), Current (A), Maximum voltage drop (%). Use one period and the units shown in the form.
Run the calculation
Enter the values and select the action. The calculation rule above explains how the inputs produce the result.
Compare a scenario
Change One-way copper circuit length (ft) on its own, keeping the other inputs fixed. Read both results before changing another assumption.
Worked example
With the example inputs listed above, the result is 2.9633 mm².
Change One-way copper circuit length (ft) from 50 to 55 while keeping every other value fixed. The result becomes 3.2597 mm². This comparison isolates that input; it does not forecast how other variables will respond.
Check the stated formula, units and limits before using the result in a decision.
Keep the displayed formula, input units and model scope with the result. Corrections or questions can be sent through the request section on this page.
Content updated: October 11, 2026