# 5 Best Free Online Internal Resistance Calculator Websites

Here is a list of the **best free online internal resistance calculator websites**. Internal resistance is the measure of how much the power source itself resists the flow of electric current. It is a natural characteristic of a power source. It is due to the resistance of the materials and internal conductivity within the power source. Due to the internal resistance of a power source, you may get lesser voltage than marked. Thus internal resistance plays an important role while designing circuits that need the correct amount of power to operate properly.

This post covers 5 free websites to calculate internal resistance. There are two ways to calculate internal resistance. One method is to measure the voltage difference between an open circuit and a closed circuit with the load resistance. And the other method needs the EML of the cell along with current and load resistance. Some of these calculators use the EML approach whereas others go with the voltage difference. You can go through the post and check these out yourself.

### My Favorite Internal Resistance Calculator

**OmniCalculator.com** is my favorite website on this list to calculate the internal resistance of an electrical source. The best thing about this calculator is that it is a multi-purpose calculator. It has 5 parameters and you can use it to calculate any of those parameters.

You can check out our other lists of the best free Online Wire Resistance Calculator Websites, Online Rolling Resistance Calculator Websites, and Parallel Resistance Calculator Online Websites.

### Comparison Table:

Name | Internal Resistance | Other Calculation | Change Unit |
---|---|---|---|

OmniCalculator.com | ✓ | EMF, V, I, R | Possible |

RedCrab-Software.com | ✓ | I | Possible |

TranslatorsCafe.com | ✓ | URL, UL, I, RL | Possible |

Calculator.academy | ✓ | - | Fixed |

Soko-heli-tools.com | ✓ | V, I, øC | Fixed |

## OmniCalculator.com

**OmniCalculator.com** has a free online internal resistance calculator. This calculator can help you calculate the resistance offered by a voltage source to the flow of current through it. In other words, it can calculate the internal resistance of a voltage source. The calculator has a nice interface along with a decent amount of theoretical definitions, examples, and explanations. The calculator itself has 5 parameters covering EML, Load Resistance, Current, Internal Resistance, and Terminal Voltage. It lets you calculate any of these parameters. You can simply add the required known values and find the values of the missing parameters.

### Internal Resistance Calculation:

**Input**: EML (V), Load Resistance (R), and Current (I).**Output**: Internal Resistance (r) and Terminal Voltage (V).

### Additional Features:

As mentioned above, this calculator can also be used to calculate EML, Load Resistance, Current, and Terminal Voltage. It also generates a link that you can use to share the calculations online.

## RedCrab-Software.com

**RedCrab-Software.com** has a free online tool to calculate the internal resistance of electrical power sources. This calculator follows the approach of comparing two different load conditions to determine the internal resistance of a power source. You have to measure the voltage when the circuit is open with no current flowing through it. Then you have to make a closed circuit with a load resister of known value. Again measure the voltage of the closed circuit. Once you have all three values, you can add that to this calculator to find the internal resistance of the power source.

### Internal Resistance Calculation:

**Input**: Open Circuit Voltage (V), Closed Circuit Voltage (V), Load Resistance (R).**Output**: Internal Resistance (r) and Current (I).

### Additional Features:

This calculator also determines the current (I) in the circuit. And for more precise results, you can set the decimal places for the output.

## TranslatorsCafe.com

**TranslatorsCafe.com** has a free online internal resistance calculator. This calculator uses the load voltage and no-load voltage methods to calculate the internal resistance of an electrical source. This includes a total of five parameters covering *No Load Voltage (UNL), Voltage with Load (UL), Load Resistance (RL), Internal Resistance (RI), and Current (I)*. The calculator has a dropdown menu where you can select what you want to calculate and from what. For internal resistance, you have to select *RI and I from UNL, RL, and UL*. Then simply add the values of UNL, RL, and UL into the calculator to get the internal resistance which is denoted by RI.

### Internal Resistance Calculation:

**Input**: No Load Voltage (UNL), Voltage with Load (UL), Load Resistance (RL).**Output**: Internal Resistance (RI) and Current (I).

### Additional Features:

This calculator has 9 calculation configurations. This allows you to calculate different combinations of parameters. You can pick what you want to calculate, add the required parameters and get the results.

## Calculator.academy

**Calculator.academy** has a free online internal resistance calculator. This calculator uses electromotive force to calculate the internal resistance of an electrical source. The calculator is on the left side of the screen and the right side covers the definition and explanation with the formula. The calculator shows the formula used at the top followed by the input parameters. It asks for *Electromotive Force (V), Current (I), and Load Resistance (R)*. You can simply provide the required values and run the calculator to get the Internal resistance (r) of the source.

### Internal Resistance Calculation:

**Input**: Electromotive Force (V), Current (I), and Load Resistance (R).**Output**: Internal Resistance (r).

## Soko-heli-tools.com

**Soko-heli-tools.com** is another free website to calculate internal resistance online. This website actually has a LiPo calculator designed to calculate the C rating (the indicator of the performance of the battery) or internal resistance of a LiPo pack. The calculator asks for the capacity of the pack along with the number of cells. then it utilizes the values of one cell of your LiPo pack. To get the internal resistance of the pack, you need to know the real-life C rating of the pack. With that, you can *Calculate iR* and get the value of internal resistance in milli-Ohms.

### Internal Resistance Calculation:

**Input**: Capacity [mAh], Cell count, and ø C rating.**Output**: Cell iR [mO], ø current [A], and voltage drop per cell [V].

### Additional Features:

You can also use this calculator to determine the real-life C rating of a battery pack when you know the internal resistance. Along with that, it also gets you the FOM, current, and voltage drop.

## Frequently Asked Questions

The internal resistance of a battery can be calculated by measuring the voltage drop across a load and the current flowing through it, and then using Ohm's law to calculate the resistance. Alternatively, the internal resistance can be calculated using a more complex method that involves measuring the open circuit voltage and the voltage under load.

Calculating the internal resistance of a 1.5 V battery needs additional information or measurements. However, we expect an AA cell to have an EMF of about 1.5 V and internal resistance of about 1 Ω.

The internal resistance of a 6 cell battery depends on the chemistry, size, age, and temperature of the battery, and can range from a few milliohms to several ohms. To determine the internal resistance of a specific 6 cell battery, you would need to measure its voltage under load and calculate the resistance using Ohm's law or use a specialized battery analyzer.

The formula for internal resistance is R_int = (V_oc - V_load) / I_load, where R_int is the internal resistance, V_oc is the open circuit voltage, V_load is the voltage under load, and I_load is the current flowing through the load. The formula for external resistance is R_ext = (V_load - V_source) / I_load, where R_ext is the external resistance, V_load is the voltage under load, V_source is the source voltage, and I_load is the current flowing through the load.

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