**The average space heater uses 1500 watts, which means it draws 12.5 amps when plugged into a 120-volt outlet. **But this draw changes if the unit is plugged into a 240-volt outlet or if the heater uses more or fewer watts.

Below, we’ll look at how to calculate the amperage of a space heater using three different methods. We’ll also talk about how to use amperage draw to understand if your breaker has enough power to safely run your electric heater.

## How Do You Calculate the Amps a Heater Draws?

Calculating the amperage of a space heater (or any other appliance, for that matter) requires knowledge of how many watts the unit uses and how many volts are supplied by the power source.

The average space heater uses 1500 watts, but this can vary by product. The most energy-efficient heaters use far less, while very powerful heaters use more.

The standard voltage of an outlet in an American home is 120 volts. Most homes also include at least one 240-volt outlet (usually for the dryer). Each breaker single pole in your breaker box feeds a run of 120-volt outlets, while 240-volt outlets require a double breaker pole.

To calculate the amperage of your space heater, you’ll need to know:

**The wattage of the unit.**This can be found printed on the bottom of the heater, on the nameplate, or in the user’s manual.**The voltage of the outlet being used.**The shape of the plug will determine what kind of outlet you must use. Standard electrical plugs are compatible with 120-volt outlets.

### Option 1: Manual Amps Calculation

Once you know these two values, the calculation to get amps is very straightforward. This is calculated using **a well known formula called ****Ohm’s Law**.

Simply divide the wattage by the voltage:

**Amps = Watts / Volts**

For example, a 1500-watt space heater plugged into a 120-volt outlet, will draw 12.5 amps.

A more energy-efficient space heater that only uses 1200 watts (plugged into a 120-volt outlet) will only draw 10 amps.

Units plugged into a 240-volt outlet will draw fewer amps compared to the same-sized unit plugged into a 120-volt outlet. For example, a 1500-watt space heater plugged into a 240-volt outlet will only draw 6.25 amps.

However, most 1500-watt (and lower) space heaters are designed to be used with 120-volt outlets. Heaters over 1500 watts are generally designed to be used with 240-volt outlets (or, more often, to be hardwired into double pole breakers).

### Option 2: Space Heater Amps Calculator

An **easier way to calculate the amperage of a space heater** is to use our handy Amperage Calculator.

Simply enter the wattage of your space heater in the box then choose the voltage. The calculator will automatically calculate the amps drawn by the unit.

This amperage calculator can also be used for other home appliances and electronic equipment.

### Option 3: Heater Amp Draw Chart

If you want to skip the math altogether, you can simply use the table below to figure out how many amps your heater will use.

Use the column on the left to find the wattage of your space heater. Then find the amperage drawn based on the voltage of the outlet it will be used with. The amperage in the middle column is for 120v outlets while the right column represents 240v outlets.

Space Heater Size | 120 volts | 240 volts |
---|---|---|

100 watts | 0.8 amps | 0.4 amps |

200 watts | 1.7 amps | 0.8 amps |

300 watts | 2.5 amps | 1.3 amps |

400 watts | 3.3 amps | 1.7 amps |

500 watts | 4.2 amps | 2.1 amps |

600 watts | 5.0 amps | 2.5 amps |

700 watts | 5.8 amps | 2.9 amps |

800 watts | 6.7 amps | 3.3 amps |

900 watts | 7.5 amps | 3.8 amps |

1000 watts | 8.3 amps | 4.2 amps |

1100 watts | 9.2 amps | 4.6 amps |

1200 watts | 10.0 amps | 5.0 amps |

1300 watts | 10.8 amps | 5.4 amps |

1400 watts | 11.7 amps | 5.8 amps |

1500 watts | 12.5 amps | 6.3 amps |

2000 watts | 16.7 amps | 8.3 amps |

3000 watts | 25.0 amps | 12.5 amps |

4000 watts | 33.3 amps | 16.7 amps |

5000 watts | 41.7 amps | 20.8 amps |

6000 watts | 50.0 amps | 25.0 amps |

7000 watts | 58.3 amps | 29.2 amps |

8000 watts | 66.7 amps | 33.3 amps |

9000 watts | 75.0 amps | 37.5 amps |

10000 watts | 83.3 amps | 41.7 amps |

11000 watts | 91.7 amps | 45.8 amps |

12000 watts | 100.0 amps | 50.0 amps |

13000 watts | 108.3 amps | 54.2 amps |

14000 watts | 116.7 amps | 58.3 amps |

15000 watts | 125.0 amps | 62.5 amps |

16000 watts | 133.3 amps | 66.7 amps |

17000 watts | 141.7 amps | 70.8 amps |

18000 watts | 150.0 amps | 75.0 amps |

19000 watts | 158.3 amps | 79.2 amps |

20000 watts | 166.7 amps | 83.3 amps |

We calculated each data point in the table below using the standard amperage equation (ohm’s law) featured in section 1. The amperage of each watt value was calculated first for 120-volt outlets, then for 240-volt outlets. As you can see, 240-volt outlets will use half as many amps as 120-volt outlets for each wattage size.

The numbers in bold represent the most likely scenarios in terms of the voltage a heater has been built to utilize. This is based on the fact that most heaters at or below 1500 watts are made to use 120-volt outlets. Anything over this size is typically hardwired or plugged into a 240-volt connection.

## Amps Draw vs Amperage of Circuit Breaker

Knowing how many amps your heater draws is important to determine if you can use it without overwhelming your circuit breaker.

Each breaker circuit in your breaker box can only handle up to a certain amperage before overheating. The breaker system is designed to cut off power if this level is exceeded.

**Most single-pole breaker circuits are rated for 15 or 20 amps**. Some can be rated for up to 30 amps, but this is less likely in a residential home. Double pole breakers can be rated for 20 to up to 60 amps.

For safety reasons, you should never surpass 80% of the maximum amp rating for each circuit (according to NEC guidelines). You can calculate what 80% of your breaker rating is by taking the amperage and multiplying it by 0.8. Or you can reference the numbers below.

- 80% of 15 amps = 12 amps
- 80% of 20 amps = 16 amps
- 80% of 30 amps = 24 amps
- 80% of 60 amps = 48 amps

**NOTE: **Keep in mind that the maximum amperage for each circuit includes all electrical devices plugged into that circuit. If only the heater is plugged into the circuit, then you only need to consider that amperage draw. But if there are other outlets being used on the same circuit, you need to add them to the amps of the heater to assure the total power used is less than 80% of the breaker’s rating.

The table below expresses the minimum circuit amp rating required for different-sized space heaters. Keep in mind, these calculations assume the heater is the only item drawing power on the circuit.

**Green** = Minimum of 15 amp breaker

**Blue** = Minimum of 20 amp breaker

**Purple** = Minimum of 30 amp breaker

**Red** = Minimum of 60 amp breaker

**Black** = Requires specialty electrical

Space Heater Size | 120 volts | 240 volts |
---|---|---|

100 watts | 0.8 amps | 0.4 amps |

200 watts | 1.7 amps | 0.8 amps |

300 watts | 2.5 amps | 1.3 amps |

400 watts | 3.3 amps | 1.7 amps |

500 watts | 4.2 amps | 2.1 amps |

600 watts | 5.0 amps | 2.5 amps |

700 watts | 5.8 amps | 2.9 amps |

800 watts | 6.7 amps | 3.3 amps |

900 watts | 7.5 amps | 3.8 amps |

1000 watts | 8.3 amps | 4.2 amps |

1100 watts | 9.2 amps | 4.6 amps |

1200 watts | 10.0 amps | 5.0 amps |

1300 watts | 10.8 amps | 5.4 amps |

1400 watts | 11.7 amps | 5.8 amps |

1500 watts | 12.5 amps | 6.3 amps |

2000 watts | 16.7 amps | 8.3 amps |

3000 watts | 25.0 amps | 12.5 amps |

4000 watts | 33.3 amps | 16.7 amps |

5000 watts | 41.7 amps | 20.8 amps |

6000 watts | 50.0 amps | 25.0 amps |

7000 watts | 58.3 amps | 29.2 amps |

8000 watts | 66.7 amps | 33.3 amps |

9000 watts | 75.0 amps | 37.5 amps |

10000 watts | 83.3 amps | 41.7 amps |

11000 watts | 91.7 amps | 45.8 amps |

12000 watts | 100.0 amps | 50.0 amps |

13000 watts | 108.3 amps | 54.2 amps |

14000 watts | 116.7 amps | 58.3 amps |

15000 watts | 125.0 amps | 62.5 amps |

16000 watts | 133.3 amps | 66.7 amps |

17000 watts | 141.7 amps | 70.8 amps |

18000 watts | 150.0 amps | 75.0 amps |

19000 watts | 158.3 amps | 79.2 amps |

20000 watts | 166.7 amps | 83.3 amps |

As you can see,** a 1500-watt space heater, the most common size, technically requires a 20-amp breaker.** If the heater is the only item drawing power from a 15 amp breaker, it is possible to run it without tripping the circuit. However, this goes against NEC safety guidelines and is not recommended.

But keep in mind, the 1500-watt rating on these heaters represents the maximum amperage the heater will draw. This means that you can safely run these heaters on a 15 amp breaker so long as you only use the low setting.