Wire Size Calculator (AWG & mm²)

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Work out the wire size you need for any AC or DC circuit from load, run length and allowable voltage drop — answer in both AWG and mm², with the governing limit shown.

Inputs

Circuit

Circuit type

System voltage (V)

Load entered as

Load current (A)

Power factor

Run and limits

One-way run length (m)

Distance from the supply to the load

Allowable voltage drop

Conductor material

Conductor temperature (°C)

Higher in conduit, roof spaces and engine bays

How to use this calculator: Wire Size Calculator (AWG & mm²)

Work out the wire size you need for any AC or DC circuit from load, run length and allowable voltage drop — answer in both AWG and mm², with the governing limit shown. The example below is calculated by this page's real engine from the displayed inputs.

1Confirm that the Wire Size Calculator (AWG & mm²) matches the quantity or design check you need.
2Enter System voltage, Load current, and Power factor using the units printed beside each field.
3Select the applicable Circuit type, Load entered as, and Allowable voltage drop 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
Circuit type	AC single-phase	Select the option that matches the real installation or scenario.
System voltage	230 V	Measured or known system voltage used by the calculation engine.
Load entered as	Current (amps)	Select the option that matches the real installation or scenario.
Load current	20 A	Measured or known load current used by the calculation engine.
Power factor	0.9	Measured or known power factor used by the calculation engine.
One-way run length	20 m	Distance from the supply to the load
Allowable voltage drop	3% — final circuits (typical)	Select the option that matches the real installation or scenario.
Conductor material	Copper	Select the option that matches the real installation or scenario.
Conductor temperature	40 °C	Higher in conduit, roof spaces and engine bays

Formula inputs & variables for Wire Size Calculator (AWG & mm²)

These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.

Variable / input	Unit	Meaning in this calculation
Circuit type	—	Select the option that matches the real installation or scenario.
System voltage	V	Measured or known system voltage used by the calculation engine.
Load entered as	—	Select the option that matches the real installation or scenario.
Load current	A	Measured or known load current used by the calculation engine.
Load power	W	Measured or known load power used by the calculation engine.
Power factor	—	Measured or known power factor used by the calculation engine.
One-way run length	m	Distance from the supply to the load
Allowable voltage drop	—	Select the option that matches the real installation or scenario.

Formula, derivation and worked example

Two things decide a conductor size: it must carry the current without overheating, and it must deliver the voltage the load expects. On short runs the ampacity limit governs; past about 20–30 metres, voltage drop takes over and is usually what forces a bigger cable. This calculator works out both, picks the smallest standard conductor that satisfies each, and tells you which of the two decided the answer — then gives the result in mm² and the nearest AWG so it is usable with either an IEC or an NEC-style specification.

I = P / (V × pf × √3 for three-phase)

ρ_T = ρ₂₀ (1 + α (T − 20))

DC / single-phase: A = 2 ρ_T L I / ΔV

Three-phase: A = √3 ρ_T L I / ΔV

Substitution steps

1. Current
given
= 20 A
2. Resistivity at temperature
ρ₂₀ (1 + α(T − 20))
= 0.01855 Ω·mm²/m
3. Allowable drop
3% × 230 V
= 6.9 V
4. Required area
2 ρ L I / ΔV
= 2.15 mm²
5. Size chosen
larger of drop and ampacity limits
= 4 mm² (12 AWG)

Computed example results

Recommended conductor: 4 mm² (12 AWG); Copper · governed by current rating
Minimum area for voltage drop: 2.15 mm²; 3% of 230 V = 6.9 V
Minimum size for current: 4 mm²; 26 A rating vs 20 A load
Design current: 20 A; single-phase, pf 0.9
Actual voltage drop: 3.71 V; 1.61% of 230 V
Nearest AWG: 12 AWG; 3.31 mm²
Power lost in the cable: 74.2 W
Cable current rating: 26 A; indicative 30 °C — derate for grouping and heat

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.

Assumptions and calculation scope

System voltage is assumed to be entered in V; converting from another unit before entry avoids changing the numerical meaning of the calculation.
Circuit type is assumed to match the real case. Choosing a different available option can change the method, factor or interpretation used by this calculator.
Wire Size Calculator (AWG & mm²) applies the displayed I = P / (V × pf × √3 for three-phase) relationship to the entered electrical inputs. Factors that are not exposed as inputs or stated assumptions are outside this calculator's calculation scope.

Common mistakes when using Wire Size Calculator (AWG & mm²)

Do not mix units for System voltage (V), Load current (A), One-way run length (m). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
Do not leave Circuit type 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 × pf × √3 for three-phase) relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
Do not treat Recommended conductor = 4 mm² (12 AWG) 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 Wire Size Calculator (AWG & mm²) is useful

Wire Size Calculator (AWG & mm²) is designed for cases where Circuit type, System voltage, Load entered as, Load current are known and you need Recommended conductor, Minimum area for voltage drop, Minimum size for current. 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 × pf × √3 for three-phase). 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.

Circuit type and System voltage: what changes the answer

The worked example uses Circuit type = AC single-phase, System voltage = 230 V, Load entered as = Current (amps), Load current = 20 A. With those values, Recommended conductor is 4 mm² (12 AWG). 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: Circuit type: Select the option that matches the real installation or scenario. Available choices include DC (battery, solar, 12/24/48 V), AC single-phase, AC three-phase. System voltage (V): Measured or known system voltage used by the calculation engine. Load entered as: Select the option that matches the real installation or scenario. Available choices include Current (amps), Power (watts). Load current (A): Measured or known load current used by the calculation engine.

How to sanity-check a Wire Size Calculator (AWG & mm²) 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 Recommended conductor, 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 Wire Gauge Chart (AWG to mm²)

Wire Gauge Chart (AWG to mm²) is directly connected from Wire Size Calculator (AWG & mm²) as a source-defined continuation or comparison.

Open Wire Gauge Chart (AWG to mm²)

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 × pf × √3 for three-phase)
ρ_T = ρ₂₀ (1 + α (T − 20))
DC / single-phase: A = 2 ρ_T L I / ΔV
Three-phase: A = √3 ρ_T L I / ΔV

Engineering notes

Single-phase and DC circuits count both conductors (2 × length); three-phase uses the √3 line-to-line relationship.
Ampacity values are indicative for insulated copper around 30 °C. Apply your own derating for grouping, ambient temperature and installation method before finalising.
Aluminium is taken as 78% of the copper current rating and 1.64× the resistance.

Quick wire size guide — copper, 3% drop, 230 V single-phase

Minimum conductor for a 3% voltage drop at 230 V single-phase and 40 °C copper. Short runs may instead be set by the ampacity of the circuit protection.

Load	10 m	20 m	30 m	50 m
6 A	1.5 mm² (16 AWG)	1.5 mm² (16 AWG)	1.5 mm² (16 AWG)	2.5 mm² (14 AWG)
10 A	1.5 mm² (16 AWG)	1.5 mm² (16 AWG)	2.5 mm² (14 AWG)	4 mm² (12 AWG)
16 A	1.5 mm² (16 AWG)	2.5 mm² (14 AWG)	4 mm² (12 AWG)	6 mm² (10 AWG)
20 A	2.5 mm² (14 AWG)	4 mm² (12 AWG)	4 mm² (12 AWG)	10 mm² (8 AWG)
32 A	4 mm² (12 AWG)	6 mm² (10 AWG)	10 mm² (8 AWG)	16 mm² (6 AWG)
50 A	10 mm² (8 AWG)	10 mm² (8 AWG)	16 mm² (6 AWG)	25 mm² (4 AWG)
63 A	16 mm² (6 AWG)	16 mm² (6 AWG)	25 mm² (4 AWG)	35 mm² (2 AWG)
100 A	25 mm² (4 AWG)	35 mm² (2 AWG)	50 mm² (1/0 AWG)	70 mm² (2/0 AWG)

Worked example

1A 20 A single-phase circuit at 230 V, 30 m away, 3% drop, copper at 40 °C.
2Allowed drop = 6.9 V; ρ₄₀ = 0.0172 × (1 + 0.00393 × 20) = 0.01855 Ω·mm²/m.
3A = 2 × 0.01855 × 30 × 20 / 6.9 = 3.23 mm² → next standard size 4 mm² (12 AWG).

Tips

If the required size looks extreme, move the distribution board closer or raise the system voltage.
Include vertical drops and routing bends in the length — cable runs are usually 20–30% longer than the straight line.

Warnings

The protective device must suit the cable: never fit a breaker larger than the conductor's derated rating.
This is a design aid, not a substitute for the local wiring code (IS 732 / IEC 60364 / NEC).

Standards & references

IEC 60364-5-52
IS 732
NEC Article 210 / 310

Frequently asked questions

What size wire do I need for 20 amps?

For a short 230 V run, 2.5 mm² (14 AWG) copper is typical; at 30 m the 3% voltage-drop limit pushes it to 4 mm² (12 AWG). At 120 V the same 20 A load needs roughly twice the copper.

Does distance change the wire size?

Yes. Beyond about 20–30 m voltage drop, not heating, decides the size — doubling the run roughly doubles the required cross-section.

How is three-phase different?

Three-phase uses √3 rather than 2 in the voltage-drop formula and carries the same power at about 58% of the single-phase current, so conductors are noticeably smaller.

What voltage drop is allowed?

IEC 60364 recommends 3% for lighting and 5% for other uses measured from the origin; the NEC suggests 3% on a branch circuit and 5% overall. Solar array wiring is usually held to 1–2%.

Can I use aluminium instead of copper?

Yes, but go up about one and a half sizes: aluminium has 64% more resistance and roughly 78% of the current rating, and it needs terminations rated for it.

Should I size on watts or amps?

Either — enter watts and the calculator converts using the voltage and power factor. Always use the continuous load, not the peak.

What inputs does the Wire Size Calculator (AWG & mm²) use?

It uses Circuit type, System voltage, Load entered as, Load current, Power factor, One-way run length, Allowable voltage drop, Conductor material, and Conductor temperature. Follow the unit printed for each field and choose any selectable option to match the real scenario.

What does the Wire Size Calculator (AWG & mm²) calculate?

It calculates Recommended conductor, Minimum area for voltage drop, Minimum size for current, Design current, Actual voltage drop, Nearest AWG, Power lost in the cable, and Cable current rating. With the displayed default inputs, Recommended conductor is 4 mm² (12 AWG).

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