DC Cable Voltage Drop Calculator

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Calculate DC cable voltage drop from system voltage, current, cable length, conductor material and cable size. Get voltage drop in volts, voltage-drop percentage, receiving-end voltage, loop resistance and cable power loss.

Inputs

DC Circuit

DC system voltage (V)

Examples: 12 V, 24 V, 48 V, 120 V, 600 V or 1000 V.

Load input

Operating current (A)

Current flowing through the complete DC circuit.

Cable Data

One-way cable length (m)

Enter the one-way physical cable route. The calculator automatically includes the return conductor.

Conductor material

Cable size

Conductor temperature (°C)

20 °C is the reference temperature. Actual conductor temperature changes resistance.

Parallel cables per polarity

Use 1 for one positive and one negative conductor. Parallel conductors reduce the effective resistance.

Allowable voltage drop (%)

Common design targets depend on the application. Enter your project limit.

How to use this calculator: DC Cable Voltage Drop Calculator

1Confirm that the DC Cable Voltage Drop Calculator matches the quantity or design check you need.
2Enter DC system voltage, Operating current, and One-way cable length using the units printed beside each field.
3Select the applicable Load input, Conductor material, and Cable size options; these choices change the calculation method or factors.
4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

Input	Example value	Why it matters
DC system voltage	12 V	Examples: 12 V, 24 V, 48 V, 120 V, 600 V or 1000 V.
Load input	Operating current (A)	Select the option that matches the real installation or scenario.
Operating current	20 A	Current flowing through the complete DC circuit.
One-way cable length	10 m	Enter the one-way physical cable route. The calculator automatically includes the return conductor.
Conductor material	Copper	Select the option that matches the real installation or scenario.
Cable size	4 mm² (12 AWG)	Select the option that matches the real installation or scenario.
Conductor temperature	20 °C	20 °C is the reference temperature. Actual conductor temperature changes resistance.
Parallel cables per polarity	1	Use 1 for one positive and one negative conductor. Parallel conductors reduce the effective resistance.
Allowable voltage drop	2 %	Common design targets depend on the application. Enter your project limit.

Formula, derivation and worked example

This calculator determines the voltage lost in a DC cable circuit using the operating voltage, current, one-way cable length, conductor material, cable cross-sectional area, conductor temperature and number of parallel conductors. Because a DC circuit has both positive and negative conductors, the one-way cable length is doubled when calculating the complete circuit resistance. Higher current, longer cable runs and smaller conductors increase voltage drop, while higher system voltage and larger conductors reduce the percentage voltage drop.

I = P / V (when load power is entered)

ρT = ρ20 × [1 + α(T − 20)]

Rloop = 2 × ρT × L / (A × Np)

Voltage Drop = I × Rloop

Voltage Drop % = (Voltage Drop / V) × 100

Receiving-End Voltage = V − Voltage Drop

Power Loss = I² × Rloop

Substitution steps

1. Operating current
Given current
= 20 A
2. Temperature-corrected resistivity
ρT = ρ20 × [1 + α(T − 20)]
= 0.01724 Ω·mm²/m
3. Complete cable path
2 × one-way length
= 20 m
4. Loop resistance
R = ρT × 2L / (A × Np)
= 0.0862 Ω
5. Voltage drop
ΔV = I × R
= 1.724 V
6. Voltage drop percentage
ΔV% = (ΔV / V) × 100
= 14.37%
7. Receiving-end voltage
Vload = V − ΔV
= 10.276 V
8. Cable power loss
P = I² × R
= 34.48 W

Computed example results

Voltage Drop: 1.724 V; 14.37% of 12 V
Voltage Drop Percentage: 14.37%; Exceeds the selected voltage-drop limit.
Receiving-End Voltage: 10.276 V; Source voltage 12 V
Loop Resistance: 0.0862 Ω; 86.2 mΩ
Power Loss: 34.48 W; 14.37% of input power
Temperature-Corrected Resistivity: 0.01724 Ω·mm²/m; Copper at 20 °C
Design Current: 20 A; User-entered operating current
Allowable Voltage Drop: 0.24 V; 2%
Minimum Size for Selected Limit: 35 mm² (2 AWG); Smallest listed size meeting 2%

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using DC Cable Voltage Drop Calculator

Do not mix units for DC system voltage (V), Operating current (A), One-way cable length (m). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
Do not leave Load input on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
Do not replace the displayed I = P / V (when load power is entered) relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
Do not treat Voltage Drop = 1.724 V from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

When the DC Cable Voltage Drop Calculator is useful

DC Cable Voltage Drop Calculator is designed for cases where DC system voltage, Load input, Operating current, One-way cable length are known and you need Voltage Drop, Voltage Drop Percentage, Receiving-End Voltage. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.

Use the calculator for the scope described by its inputs and notes. The displayed method is I = P / V (when load power is entered). If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.

DC system voltage and Load input: what changes the answer

The worked example uses DC system voltage = 12 V, Load input = Operating current (A), Operating current = 20 A, One-way cable length = 10 m. With those values, Voltage Drop is 1.724 V. Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.

For this calculator, the main input roles are: DC system voltage (V): Examples: 12 V, 24 V, 48 V, 120 V, 600 V or 1000 V. Load input: Select the option that matches the real installation or scenario. Available choices include Operating current (A), Load power (W). Operating current (A): Current flowing through the complete DC circuit. One-way cable length (m): Enter the one-way physical cable route. The calculator automatically includes the return conductor.

How to sanity-check a DC Cable Voltage Drop Calculator result

Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Voltage Drop, because it is the first worked-example output shown by the live engine.

Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.

Next logical calculator

Continue with DC Cable Size Calculator (12V / 24V / 48V)

Useful next check because both tools use Load power and Allowable voltage drop, while DC Cable Size Calculator (12V / 24V / 48V) answers a different part of the same workflow.

Open DC Cable Size Calculator (12V / 24V / 48V)

Standards, source trail and limitations

References show the method used. Check the current local edition, amendments and project specification before a regulated decision.

Formula

I = P / V (when load power is entered)
ρT = ρ20 × [1 + α(T − 20)]
Rloop = 2 × ρT × L / (A × Np)
Voltage Drop = I × Rloop
Voltage Drop % = (Voltage Drop / V) × 100
Receiving-End Voltage = V − Voltage Drop
Power Loss = I² × Rloop

Engineering notes

The entered cable length is one-way. Both positive and negative conductors are included automatically.
Copper resistivity is approximately 0.01724 Ω·mm²/m at 20 °C.
Aluminium resistivity is approximately 0.02826 Ω·mm²/m at 20 °C.
Conductor resistance increases as conductor temperature rises.
Parallel conductors reduce effective resistance when the conductors are equal in size and share current properly.
Voltage-drop limits are application-dependent. Always use the project specification or applicable design standard.

DC Voltage Drop Reference Guide

Use this as a quick reference only. Actual voltage drop depends on voltage, current, cable length, material, cable size and conductor temperature.

System	Typical Application	Common Voltage-Drop Target
12 V DC	Battery, RV, automotive, small off-grid	2–3%
24 V DC	Battery banks, telecom, off-grid	2–3%
48 V DC	Battery systems, inverter DC input	1–3%
120–600 V DC	Solar PV and industrial DC	Project-specific
600–1000 V DC	Utility and commercial PV	Project-specific

Formulas explained

Rloop = 2 × ρT × L / (A × Np)

The positive and negative conductors both carry the current, so the electrical path is twice the entered one-way length. Parallel conductors divide the effective resistance.

Rloop: Complete DC loop resistance, Ω
ρT: Conductor resistivity at operating temperature, Ω·mm²/m
L: One-way cable length, m
A: Cable cross-sectional area per conductor, mm²
Np: Number of parallel conductors per polarity

ΔV = I × Rloop

Ohm's law is used to calculate the voltage lost across the complete DC cable loop.

ΔV: DC cable voltage drop, V
I: Operating current, A
Rloop: Complete positive + negative loop resistance, Ω

ΔV% = (ΔV / V) × 100

Voltage drop percentage compares the voltage lost in the cable with the source operating voltage.

ΔV: Voltage drop, V
V: DC system voltage, V

P_loss = I² × Rloop

The resistive heating loss in the complete cable loop is calculated using the I²R relationship.

P_loss: Cable power loss, W
I: Operating current, A
Rloop: Complete loop resistance, Ω

DC Cable Size Calculator

Perform detailed DC cable sizing based on voltage drop and cable current requirements.

Solar Wire Size Calculator

Estimate suitable cable sizes for solar PV applications.

12V Wire Size Chart

Compare common 12 V, 24 V and 48 V cable sizes for different currents and cable lengths.

Worked example

1Example: A 48 V DC system supplies 20 A through a 20 m one-way copper cable using 6 mm² conductors at 20 °C.
2The complete electrical path is 40 m because both positive and negative conductors carry current.
3Loop resistance = 2 × 0.01724 × 20 / 6 = 0.11493 Ω.
4Voltage drop = 20 × 0.11493 = 2.299 V.
5Voltage drop percentage = (2.299 / 48) × 100 = 4.79%.
6Receiving-end voltage = 48 − 2.299 = 45.701 V.
7If the design limit is 2%, the 6 mm² cable does not satisfy the selected voltage-drop limit and a larger cable should be considered.

Assumptions

The entered cable length is one-way.
Both positive and negative conductors have the same cross-sectional area.
Parallel conductors are assumed to share current equally.
The calculation is based on conductor resistance and does not model connector, fuse, breaker, terminal or equipment contact resistance.
Cable ampacity is not determined by this calculator.
Final cable selection must consider ampacity, installation method, insulation rating, ambient temperature, grouping, protection and applicable standards.

Tips

Use the actual routed cable length rather than the straight-line distance.
If voltage drop is too high, increase the cable size, reduce the cable length or increase the DC system voltage where appropriate.
Low-voltage systems such as 12 V are much more sensitive to voltage drop than higher-voltage DC systems.
For long solar DC runs, evaluate both voltage drop and conductor thermal capacity.

Warnings

This calculator determines DC voltage drop and cable resistive loss; it is not a complete cable ampacity or protection design tool.
For solar PV systems, also verify maximum operating voltage, short-circuit current, cable temperature rating, installation conditions and applicable PV requirements.
For battery-to-inverter cables, high fault current and short-circuit protection require separate engineering verification.
Always verify the final cable selection against manufacturer data and the applicable electrical standard.

Standards & references

IEC 60364-5-52
IEC 62548
NEC Article 690

Frequently asked questions

What is DC cable voltage drop?

DC cable voltage drop is the reduction in voltage caused by the electrical resistance of the positive and negative conductors. It increases with current and cable length and decreases with larger conductor size.

How is DC cable voltage drop calculated?

For a basic two-conductor DC circuit, voltage drop is calculated as ΔV = I × R, where R is the total resistance of the positive and negative cable path. Cable resistance can be calculated from conductor resistivity, length and cross-sectional area.

Does the calculator use one-way or total cable length?

Enter the one-way cable length. The calculator automatically doubles the length because the DC circuit includes both the outgoing and return conductors.

Why is voltage drop more important in 12V systems?

The same voltage loss represents a much larger percentage of a 12 V supply than a higher-voltage system. Therefore, low-voltage DC systems often require larger conductors to maintain an acceptable voltage-drop percentage.

What percentage of voltage drop is acceptable?

The acceptable value depends on the application and project requirements. Common design targets are around 1–3%, but the applicable standard, equipment manufacturer and project specification should determine the final limit.

Does cable temperature affect DC voltage drop?

Yes. Conductor resistance increases as temperature increases. A hotter conductor therefore produces a higher voltage drop for the same current, length and cable size.

What happens if DC voltage drop is too high?

Excessive voltage drop reduces the voltage available at the load, increases cable power loss and can affect equipment performance. Increasing cable size, reducing cable length or using a higher system voltage can reduce the percentage voltage drop.

Can this calculator be used for solar cables?

Yes. It can provide an indicative voltage-drop calculation for DC PV cable runs. However, solar PV cable selection must also consider current carrying capacity, environmental conditions, insulation rating, connectors, protection and applicable PV standards.

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