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:

• P_single-phase = U*I*cos φ

• S_single-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:

• P_three-phase = U*I*cos φ*√3
• S_three-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.
P_single-phase =U*I*cos φ [W]

The apparent power S (in volt-amperes) equals the voltage (in volts) multiplied by the current (in amperes).
S_single-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.
P_three-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.

S_three-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:
S_three-phase = P_three-phase/cos φ