Electrical Cable Size Calculator

Use our free Cable Sizing Calculator for High/ Medium Voltage power cables

There are a variety of cables available in the market in various sizes. However, to decide which size will be appropriate for your application you require an Electrical Cable Size Calculator. It helps you understand the best fit size for your requirement. It is calculated against IEC and British standards. A power factor of 0.8 is used in calculating The KW. Cable Sizing Calculator 230V and 415V Voltage Drop.

To calculate the Cable Sizing one needs to divide the voltage running through the cable by the target current. For instance, If your wire has a voltage current of 150 Volts and your target is 30 then you divide 150/30. This gives you your target resistance of 5 which is required. Electrical Cable Size Calculator helps in calculating it in large numbers.

When you are searching for wires for your home and domestic lighting then usually 1.5mm or 1mm is used. However, in most cases, an Electrical Cable Sizing of 1mm is more than enough. 1.5 should be used only when cable run is over a long distance and to cope with supply demand and voltage drop.

Electrical Cable Size Calculator

While selecting a cable Electrical Cable Sizing Chart helps you make a better and informed decision. These charts help in deciding the size of cable required for your application. For instance, if a small sized cable is used then it may melt due to the heavy flow of current. Hence Cable Sizing Chart helps in determining the size and the diameter. The smaller the diameter the higher it will resist the energy flow.

The Medium Voltage Cable Sizing has a voltage rating of 1KV to 100 VK. They have highly engineered connections that need to be cut properly. If they are not cut properly they may blow up and injure personnel or equipment. The concept of Mv Cable Sizing was introduced due to the increase in demand for a level of voltage. As the demand increased so did the classification. These days extra low and extra high classifications are also available

Cable with different amounts of electrical resistance are used in different applications hence Power Cable Size Calculator helps in determining the size of the cable required to avoid any mishap.

Electrical Cable Size Calculation Formula is tedious and complicated hence we get you the simplest way to calculate the size appropriate for your application. We use the Bs7671 Cable Sizing method to calculate the size which is the British standard for the current carrying capacity of single core armoured XLPE insulated copper cable.


Electrical Cable Size Calculator

Supply Type

Cable Run


Recommended cables sizes are based upon information given by user and are intendend to use as guide only. Above calculation is derived from BS7671 Requirements for IEE Wiring Regulations, Installation method C, for cable types BS5467 and BS6724 and is bease on voltage drop selected at 230 and 400 volts


Electrical Cable Sizing Chart

  • Step 1. DC Amps: Locate the flow of current in amps of your circuit along the top of the chart below.
  • Step 2. Circuit Type: Select the correct type of circuit. Examples of Non Critical circuit are bait pumps, windlasses, general lighting, general appliances. Examples of Critical circuits are bilge blowers, panel main feeders, navigation lights, electronics.
  • Step 3. Cable Length: Find the correct length range of cables. Please note that the length is the total length of the positive and negative wires. I.E. Distance from battery to appliance multiplied by 2.
  • Step 4. Correct Cable Size: Intersect the DC Ampere with the cables length range to identity the correct coloured symbol.

Electrical Cable Size

Electrical Cable Size



Cables impedance calculation

Impedance is calculated by below formula:

Z c = R c 2 + X c 2

This method calculates the impedance when the cable and load power factor is the same, this scenario is worse case power factor.

cable sizing calculator uses the resistance Rc from Table 35 in AS/NZS 3008-2017. The reactance for single core cables is selected from the flat


Loop impedance calculation

The maximum loop distance is calculated by below formula:

L m a x = 0.8 V 1 ϕ 1000 I m i n Z c


  • V is the single phase voltage.
  • Imin is the minimum alowable tripping current of the MCB or other protection device.
  • Zc is the cable impedance in Ohm/km.


Voltage drop calculation

The three phase AC voltage drop is calculated as below

V d 3 ϕ = I L ( 3 Z c ) 1000

The single phase AC voltage drop is calculateda as below

V d 1 ϕ = I L ( 2 Z c ) 1000

Where I is the load current, L is the distance, and Zc is the cable impedance in Ohm/km.


Short circuit calculation

The short circuit capacity of the cables is calculated according to AS/NZS 3008-2017

I 2 t = K 2 S 2


  • I is the short circuit current capacity in amperes,
  • K is a constant that is selected from Table 52 in AS/NZS 3008-2017.
  • S is the cross sectional area of the conductor.
  • t is the short circuit duration in seconds.


Electrical Cables Size & Current Rating Chart

Cross Section (mm2) Approximate Overall Diameter (mm) Current Rating
Single Phase (Amps) Three Phase (Amps)
1.5 2.9 17.5 15.5
2.5 3.53 24 21
4 4.4 32 28
6 4.68 41 36
10 5.98 57 50
16 6.95 76 68
25 8.7 101 89
35 10.08 125 110
50 11.8 151 134
70 13.5 192 171
95 15.7 232 207
120 17.4 296 239
150 19.3 300 262
185 21.5 341 296
240 24.6 400 346
300 27.9 458 394
400 30.8 546 467
500 33.8 626 533
630 37.6 720 611
International standard wire size Chart (IEC 60228)
0.75 mm² 4 mm² 0.5 mm² 1 mm² 2.5 mm² 1.5 mm²
70 mm² 6 mm² 25 mm² 185 mm² 35 mm² 400 mm²
95 mm² 1000 mm² 10 mm² 800 mm² 150 mm² 50 mm²
300 mm² 120 mm² 500 mm² 16 mm² 630 mm² 240 mm²