Free · Physics models
Resistive Wire Voltage Drop
Estimate resistive voltage loss, relative voltage drop and remaining load voltage from wire geometry and current.
- Formula & worked example
- Private in your browser
- No signup
Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
With the retained copper resistivity 1.72 × 10⁻⁸ Ω·m, a 10 m run, 10 mm² area, 10 A DC and one conductor per leg give 0.344 V drop, 0.344% of 100 V, leaving 99.656 V.
ΔV = I ρ L × phase factor/(A N); load voltage = supply voltage − ΔV.
Worked example
Enter these known values and leave the other values blank.
- One-way wire run length
- 10 m
- Cross-sectional area
- 10 mm²
- Initial voltage
- 100 V
- Load current
- 10 A
- Identical parallel conductors per leg
- 1
- Voltage drop
- 0.344 V
- Voltage drop as a percentage
- 0.344 %
- Voltage at the end
- 99.7 V
Assumptions and limitations
- The DC and single-phase path use twice the one-way wire length. Balanced three-phase uses the retained approximate factor √3.
- Resistivity and AWG areas are captured approximate reference values; conductor temperature, contact resistance, skin effect and reactance are omitted.
- The single-phase factor 2.00000000001 contains a tiny retained selection marker. It is an approximation to a two-leg path, not extra impedance physics.
- Parallel conductor count is a positive integer per leg. The model uses nonnegative current magnitude and positive supply voltage.
- This constant-current estimate does not solve a load impedance or certify a wiring installation. A negative resulting load voltage means the requested current is incompatible with a simple positive-voltage load.
- Enter known quantities and clear the unknown for available inverse branches. Locks retain supplied values; incompatible fully visible identities generate consistency messages.
Common questions
Which wire length belongs in the input?
Use one-way run length. The selected phase factor includes the return path for DC and single-phase circuits.
What does the number of conductors mean?
It is the count of identical parallel conductors per leg. Equal current sharing is assumed.
How do presets affect the result?
Material resistivity and AWG areas are approximate. A custom cross section can be supplied directly; changing the wire-size preset replaces that area.
References
Bookify requires positive supply voltage, nonnegative load-current magnitude and a positive integer parallel-conductor count for the retained resistive voltage-drop model.