In order to convert current intensity (in amperes [A]) into active power (in watts [W]) and apparent power (in volt-amperes [VA]), you have to know the voltage of the mains.
 
In the charts below, you will find a quick conversion of the number of amperes.
 
Attention: we use cos φ = 0.8. If you are dealing with a different cos φ, you can use the formulas for calculating the active power. 


Single-phase:
I [A] U = 115V U = 230V
Psingle-phase [W]Ssingle-phase [VA]Psingle-phase [W]Ssingle-phase [VA]
0.1 9.2 11.5 18.4 23
0.25 23 28.75 46 57.5
0.5 46 57.5 92 115
0.75 69 86.25 138 172.5
1 92 115 184 230
1.25 115 143.75 230 287.5
1.5 138 172.5 276 345
1.75 161 201.25 322 402.5
2 184 230 368 460
2.25 207 258.75 414 517.5
2.5 230 287.5 460 575
2.75 253 316.25 506 632.5
3 276 345 552 690
3.25 299 373.75 598 747.5
3.5 322 402.5 644 805
3.75 345 431.25 690 862.5
4 368 460 736 920

Used formulas:
    • Psingle-phase = U*I*cos φ
    • Ssingle-phase = U*I

Three-phase:
I [A] U = 230V U = 400V
Pthree-phase [W]Sthree-phase [VA]Pthree-phase [W]Sthree-phase [VA]
0.1 31.87 39.84 55.43 69.28
0.25 79.67 99.59 138.56 173.21
0.5 159.35 199.19 277.13 346.41
0.75 239.02 298.78 415.69 519.62
1 318.70 398.37 554.26 692.82
1.25 398.37 497.96 692.82 866.03
1.5 478.05 597.56 831.38 1039.23
1.75 557.72 697.15 969.95 1212.44
2 637.39 796.74 1108.51 1385.64
2.25 717.07 896.34 1247.08 1558.85
2.5 796.74 995.93 1385.64 1732.05
2.75 876.42 1095.52 1524.20 1905.26
3 956.09 1195.11 1662.77 2078.46
3.25 1035.77 1294.71 1801.33 2251.67
3.5 1115.44 1394.30 1939.90 2424.87
3.75 1195.11 1493.89 2078.46 2598.08
4 1274.79 1593.49 2217.02 2771.28
 
Used formulas:
  • Pthree-phase = U*I*cos φ*√3
  • Sthree-phase = U*I*√3
 
When determining the power of the load, we first check whether it is a single-phase or a three-phase load.

Single-phase:
The active power P (in watts) equals the voltage (in volts) multiplied by the current (in amperes) and cos φ.
Psingle-phase =U*I*cos φ [W]

The apparent power S (in volt-amperes) equals the voltage (in volts) multiplied by the current (in amperes).
Ssingle-phase = U*I [VA]

Three-phase:
The active power P (in watts) equals the voltage (in volts) multiplied by the current (in amperes), cos φ and the square root of three.
Pthree-phase = U*I*cos φ*√3 [W]

 
The apparent power S (in volt-amperes) equals the voltage (in volts) multiplied by the current (in amperes) and the square root of three.


Sthree-phase = U*I*√3 [VA]

If you want to convert active power P in watts (W) into apparent power S in volt-amperes (VA), you can use this formula:
Sthree-phase = Pthree-phase/cos φ