Convert Watts to Amps and Amps to Watts  How to Calculate Watts
Conversions between electrical units are usually simple and straightforward  take a formula, write down values, and let the calculator do the rest.
However, in real life, things are not always that simple, especially when converting units that require at least one unit to be known. If You wish to know more about converting watts to amps, amps to watts, voltamps to watts, and similar, read carefully...
On This Page:
 How to Convert Amps to Watts, Watts to Amps and Other Formulas
 Watts to Amps and Amps to Watts Conversion Examples
 Watts to Amps and Amps to Watts Conversion Calculators
 Watts to Amps Chart
 Amps to Watts Chart
 Constant Current Discharge vs Constant Power Discharge Charts
How to Convert Amps to Watts, Watts to Amps and Other Formulas
Before diving into math and physics, it is important to know which unit is used for what:
 'I': current strength, measured in Amps (A),
 'P': power, measured in Watts (W),
 'U': potential difference, measured in Volts (V),
 'E': energy, measured in Joules (J), although sometimes measured in Wh (WattHours),
 'T': time, measured in seconds (s) and sometimes in hours (h).
In order to convert Amps (A) to Watts (W) and Watts (W) to Amps (A) one must use two different (although similar) formulas, one for Direct Current (DC) and another for Alternate Current (AC):
DC:
P (W) = I (A) * U (V)
AC:
P (W) = I (A) * U (V) * cos α
Note: α is the phase angle between voltage and current  in DC electric systems α=0° (cos 0°=1), while in AC electric systems α depends on the type of load (inductive or capacitive)  this is Effective Power of AC electric system and is expressed by Watts.
Apparent Power of AC systems is expressed in VoltAmps (never in watts) and is obtained by multiplying Volts and Amps.
In order to simplify things, very often phase shift in AC systems is considered to be 0°  this is acceptable for some quick calculations, but it may not be sufficient for systems with large inductive or capacitive loads.
So, if in order to convert:
 Amps to Watts, one also needs Volts: P (W) = I (A) * U (V)
 Watts to Amps, one also needs Volts: I (A) = P (W) / U (V)
 Volt and Amps to Watts: P (W) = I (A) * U (V)
 Volts to Amps, one also needs Watts: I (A) = P (W) / U (V)
 Amps to Volts, one also needs Watts: U (V) = P (W) / I (A)
 WattHours to Amp Hours, one also needs Volts: E (Wh) = Capacity (Ah) * U(V)
Watts to Amps and Amps to Watts Conversion Examples
Here are several Watts to Amps and Amps to Watts conversion examples:
12 Volts and 0.15 Amps to Watts: P(W) = U(V) * I(A) = 12 * 0.15 = 1.8 W
24 Volts and 37 Amps to Watts: P(W) = U(V) * I(A) = 24 * 37 = 888 W
36 Volts and 2400 Watts to Amps: I(A) = P(W) / U(V) = 2400 / 36 = 66.66 Amps
120 Volts and 4800 Watts to Amps: I(A) = P(W) / U(V) = 4800 / 120 = 40 Amps
Watts to Amps and Amps to Watts Conversion Calculators
In order to convert Watts to Amps and Amps to Watts, feel free to use these conversion calculators  write the values that You have and click 'Calculate' to convert them.
Note: It is assumed that the electric system is DC or that at least the α is 0° (cos α = cos 0°= 1):
Watts to Amps 
Amps to Watts 

Watts: Volts: Amps: 
Amps: Volts: Watts: 
Watts to Amps Chart
The following Watts to Amps chart lists electric currents (given in Amps) of specific loads, depending on the nominal voltage (α=0°, cos 0°=1):
Power (Watts)  Power (HP)  Current @ Nominal Voltage  
12 Volts  24 Volts  36 Volts  120 Volts  230 Volts  
250 W  0.335 HP  20.83 A  10.41 A  6.94 A  2.083 A  1.087 A 
500 W  0.67 HP  41.67 A  20.83 A  13.89 A  4.167 A  2.174 A 
746 W  1 HP  62.16 A  31.08 A  20.72 A  6.216 A  3.243 A 
1000 W  1.34 HP  83.33 A  41.66 A  27.78 A  8.333 A  4.238 A 
1492 W  2 HP  124.3 A  62.16 A  41.44 A  12.43 A  6.487 A 
2000 W  2.68 HP  166.6 A  83.3 A  55.5 A  16.66 A  8.695 A 
2238 W  3 HP  186.5 A  93.25 A  62.16 A  18.65 A  9.730 A 
2984 W  4 HP  248.6 A  124.3 A  82.88 A  24.86 A  12.97 A 
3730 W  5 HP  310.8 A  155.4 A  103.6 A  31.08 A  16.21 A 
5000 W (5 kW)  6.70 HP  416.6 A  208.3 A  138.8 A  41.6 A  21.74 A 
10 kW  13.40 HP  833.3 A  416.6 A  277.8 A  83.3 A  43.48 A 
Note: when calculating these values, we have used 1 HP = 746 watts.
For example: if you have a 36V load that requires 3 HP (~2238 W), that load will draw ~62.16 A of current.
2000 Watts to Amps
If You plan on having a 2000 Watts load (power generator, power inverter, UPS device, etc.), it is recommended to know the required current (A or Amps) and voltage (V)  the higher the voltage, the less current is required, leading to thinner cables or less energy loses. However, higher voltages can be harmful. The following chart lists required (2000 Watts to) Amps for most commonly used voltages.
Voltage (V)  12V  24V  36V  48V  120V  230V 
Current (A)  166.6A  83.3A  55.5A  41.6A  16.66A  8.695A 
As one can see, if the nominal voltage is increased from 12V to 48V, the current is decreased 4x, leading to a rather acceptable current of 41.66 Amps (from 166.6A!).
3000 Watts to Amps
Similarly, if the load is 3000W or even larger, higher voltages are required in order to keep the current at acceptable levels:
Voltage (V)  12V  24V  36V  48V  120V  230V 
Current (A)  250A  125A  83.3A  62.5  25A  13.04A 
In order to find out exact voltages, currents and wattages, feel free to use our Watts to Amps and Amps to Watts conversion calculators.
Amps to Watts Chart
The following Amps to Watts chart lists power values given in Watts, depending on the specific current and nominal voltage (α=0°, cos 0°=1):
Current (Amps)  Power @ Nominal Voltage  
12 Volts  24 Volts  36 Volts  120 Volts  230 Volts  
1 A  12 W  24 W  36 W  120 W  230 W 
2 A  24 W  48 W  72 W  240 W  460 W 
5 A  60 W  120 W  180 W  600 W  1150 W 
10 A  120 W  240 W  360 W  1200 W  2300 W 
25 A  300 W  600 W  900 W  3000 W  5750 W 
50 A  600 W  1200 W  1800 W  6000 W  11500 W 
100 A  1.2 kW  2.4 kW  3.6 kW  12 kW  23 kW 
200 A  2.4 kW  4.8 kW  7.2 kW  24 kW  46 kW 
500 A  6 kW  12 kW  18 kW  60 kW  115 kW 
1000 A  12 kW  24 kW  36 kW  120 kW  230 kW 
For example: if you have a 36V motor that is rated at 50 Amps, its nominal power is 1800 watts.
Constant Current Discharge vs Constant Power Discharge Charts
As the batteries are being discharged, their voltage drops due to the increase in internal resistance. Thus, in order to check how good is the battery, one often has to check both the Constant Current Discharge Chart and Constant Power Discharge Chart of the battery.
Note: not all manufacturers provide this information.
For example: The following chart lists constant current discharge values for Renogy RNGBATTAGM12100 battery, given in Amps, measured at 77°F (25°C):
End Voltage (V/Cell) 
End Voltage (V/Battery) 
5 min  10 min  15 min  20 min  30 min  45 min  1 hour  2 hours  3 hours  4 hours  5 hours  6 hours  8 hours  10 hours  20 hours 
1.60  9.6  330.8  232.5  188.5  154.3  112.3  80.5  63.8  37.5  27.6  22.2  18.6  16.2  12.7  10.5  5.45 
1.65  9.9  291.7  215.1  178.5  146.6  106.7  77.4  61.9  36.3  26.7  21.7  18.3  15.9  12.6  10.3  5.40 
1.70  10.2  261.6  199.5  165.1  138.9  101.8  74.6  59.5  35.3  26.0  21.2  17.9  15.6  12.4  10.2  5.34 
1.75  10.5  237.0  186.3  154.0  130.8  96.5  71.3  57.1  34.4  25.4  20.7  17.6  15.3  12.2  10.1  5.29 
1.80  10.8  210.0  167.6  143.7  123.5  92.1  68.7  55.1  33.1  24.6  20.2  17.2  15.0  12.0  10.0  5.20 
1.85  11.1  173.6  146.4  130.2  115.3  87.5  65.2  52.4  31.3  23.5  19.2  16.4  14.4  11.6  9.65  5.13 
End Voltage (V/Cell) 
End Voltage (V/Battery) 
10 min  30 min  1 hour  5 hours  10 hours  20 hours 
1.60  9.6  232.5  112.3  63.8  18.6  10.5  5.45 
1.65  9.9  215.1  106.7  61.9  18.3  10.3  5.40 
1.70  10.2  199.5  101.8  59.5  17.9  10.2  5.34 
1.75  10.5  186.3  96.5  57.1  17.6  10.1  5.29 
1.80  10.8  167.6  92.1  55.1  17.2  10.0  5.20 
1.85  11.1  146.4  87.5  52.4  16.4  9.65  5.13 
Also, the following chart lists constant power discharge values for Renogy RNGBATTAGM12100 battery, given in Watts, measured at 77°F (25°C):
End Voltage (V/Cell) 
End Voltage (V/Battery) 
5 min  10 min  15 min  20 min  30 min  45 min  1 hour  2 hours  3 hours  4 hours  5 hours  6 hours  8 hours  10 hours  20 hours 
1.60  9.6  3473  2509  2070  1719  1266  917  734.4  426.6  316.2  255.6  215.4  187.8  148.8  123.0  64.2 
1.65  9.9  3115  2348  1981  1647  1211  886  714.6  415.2  307.8  250.8  211.8  184.8  142.2  121.8  63.6 
1.70  10.2  2825  2199  1846  1570  1161  858  690.0  405.6  300.6  246.0  208.8  182.4  145.8  120.6  63.0 
1.75  10.5  2587  2069  1732  1486  1105  823  664.8  396.0  294.6  240.6  205.6  179.4  144.0  119.4  62.4 
1.80  10.8  2318  1873  1626  1410  1060  796  643.2  382.8  286.2  235.2  201.6  176.4  142.2  118.8  61.8 
1.85  11.1  1935  1649  1482  1323  1011  758  613.2  364.8  274.2  225.0  193.2  169.2  137.4  114.6  61.2 
End Voltage (V/Cell) 
End Voltage (V/Battery) 
10 min  30 min  1 hour  5 hours  10 hours  20 hours 
1.60  9.6  2509  1266  734.4  215.4  123.0  64.2 
1.65  9.9  2348  1211  714.6  211.8  121.8  63.6 
1.70  10.2  2199  1161  690.0  208.8  120.6  63.0 
1.75  10.5  2069  1105  664.8  205.6  119.4  62.4 
1.80  10.8  1873  1060  643.2  201.6  118.8  61.8 
1.85  11.1  1649  1011  613.2  193.2  114.6  61.2 
Typically for leadacid batteries, the Renogy AGM battery loses its effective capacity as the discharge current is increased.
As one can see, values in these two charts differ, depending on the discharge type  this is very important for all the loads being powered by the batteries, regardless if they are powered directly or via some power inverter.
For example: the Renogy RNGBATTAGM12100 battery is able to power 205.6 watts load for 5 hours, without the voltage dropping below 10.5 volts  during these 5 hours, both voltage and current changes over time in order to provide the required 205.6 watts of power.
Long Story Short: When calculating watts (power), one must know Amps (current) and Volts (voltage). If the electric system is AC (Alternate Current) it is important to know if the load has large impedance/capacitance and how it changes the phase angle (shift) between current and voltage  for quick checks, one may assume that phase shift is 0°, but this is only an approximation.
When converting Wh (energy given in watthours) to Ah (capacity given in Amphours) and back, one also must know the nominal voltage of the system.
If the power source of the electric system is a leadacid battery, and the discharge time is shortened, so is the effective capacity of the battery decreased.