Cable Voltage-Drop Sizing Planner
Calculate the theoretical conductor area required by a user-selected voltage-drop limit. This is not a code-compliant cable selection.
Use the Cable Size Calculator
Calculate the theoretical conductor area required by a user-selected voltage-drop limit. This is not a code-compliant cable selection.
Calculations happen locally in your browser. ToolLott does not send these inputs to a server for this tool.
Preliminary engineering calculation only. It does not replace applicable codes, manufacturer data, licensed electrical or mechanical design, protection studies, derating, fault checks, site conditions or professional verification.
How to use it
Replace the worked-example values with the actual project inputs. Review the intermediate quantities and assumptions before using the result elsewhere.
How the Cable Size Calculator works
Calculate the theoretical conductor area required by a user-selected voltage-drop limit. This is not a code-compliant cable selection. The methodology below exposes the production equation, a QA-verified worked example and the boundary between this screen and detailed design.
Calculation breakdown
ToolLott will explain the current inputs and displayed result here.
Theoretical conductor area from voltage-drop limit
The production engine evaluates A = k rho L I / DeltaV, where k=2 single-phase/DC or sqrt(3) three-phase. It begins by convert the allowed voltage-drop percentage to volts., then choose the circuit factor for single-phase/DC or balanced three-phase., and finally solve the resistive voltage-drop relationship for conductor area and compare with the next common nominal size. This keeps the calculation auditable instead of hiding design assumptions behind a single number.
A = k rho L I / DeltaV, where k=2 single-phase/DC or sqrt(3) three-phaseToolLott evaluates the relationship using the entered units and full numeric precision before display rounding.
| Symbol / input | Meaning | Unit |
|---|---|---|
current | Load current (A) | user input |
voltage | System voltage (V) | user input |
length | One-way cable length (m) | user input |
drop | Maximum voltage drop (%) | user input |
resistivity | Conductor resistivity (ohm mm2/m) | user input |
phase | Circuit arrangement | user input |
Step-by-step method
- Convert the allowed voltage-drop percentage to volts.
- Choose the circuit factor for single-phase/DC or balanced three-phase.
- Solve the resistive voltage-drop relationship for conductor area and compare with the next common nominal size.
Worked example
Aisha, a project engineer, has a 32 A, 230 V single-phase load on a 45 m cable run and wants a preliminary conductor-size screen before formal electrical design.
Example inputs
- Load current (A): 32
- System voltage (V): 230
- One-way cable length (m): 45
- Maximum voltage drop (%): 3
- Conductor resistivity (ohm mm2/m): 0.0175
- Circuit arrangement: single
Calculation / processing
Allowed drop = 230 x 3% = 6.9 V.A = 2 x 0.0175 x 45 x 32 / 6.9 = 7.304 mm².The next common nominal size shown by the screen is 10 mm², before ampacity/derating/code checks.
Use the result as a screening or quantity-planning value and compare it with the project criteria, manufacturer data and applicable engineering requirements before making a design or procurement decision.
Assumptions
- The entered values are representative of the condition being screened and use the units shown on the page.
- The equation models only the stated relationship; omitted system effects are not silently estimated.
Limitations
- This page is not engineering certification and does not replace applicable standards, design loads, manufacturer data, site investigation or competent professional review.
- Results can change materially when real geometry, losses, transients, material properties, duty cycles, safety factors or regulatory criteria differ from the simplified inputs.
Common questions
Is this a final engineering design?
No. It is a transparent screening calculation using the entered assumptions and the stated equation.
Why does the page show assumptions and limitations?
Engineering formulas are only valid within their modelling assumptions; exposing them helps users decide what additional design checks are required.
Should I use the rounded displayed value in later design work?
Use suitable calculation precision and the governing project/standard requirements rather than relying on display rounding alone.
Methodology sources
Related ToolLott tools
A realistic way Aisha could use this tool
Aisha is a project engineer.
Aisha has a 32 A, 230 V single-phase load on a 45 m cable run and wants a preliminary conductor-size screen before formal electrical design.
For this case the entered data is current = 32; voltage = 230; length = 45; drop = 3; resistivity = 0.0175; phase = “single”. The page evaluates that exact set and reports Voltage-drop area (theoretical): 7.304 mm2; the example therefore demonstrates the method with real values rather than describing a vague before-and-after story.
This produces Voltage-drop area (theoretical): 7.304 mm2. In practical terms, Aisha can calculate the theoretical conductor area required by a user-selected voltage-drop limit. This is not a code-compliant cable selection using a result tied to the shown inputs instead of an unexplained recommendation. The page also keeps this limitation explicit: Preliminary screening or quantity calculation only.
Fictional scenario using realistic example data. For Ready tools, the worked result is tied to the tested example shown in the tool. Replace the figures with your own inputs and independently verify important professional, financial, legal, health or safety decisions.
What this calculator is for
Use it to calculate the theoretical conductor area required by a user-selected voltage-drop limit. This is not a code-compliant cable selection.
It sits within ToolLott’s Electrical collection, where you can also estimate battery banks, cable sizes, generator sizes, motor current, Ohm’s law values, solar systems, transformers and voltage drop.
Cable Voltage-Drop Sizing Planner
Use the theoretical result as a screening step before checking installation method, current capacity, temperature, fault protection and the applicable wiring rules.
Not a code-compliant cable selection. Confirm current-carrying capacity, installation conditions, correction factors, protective devices and local standards with a qualified person.