Ways to calculate bacteria growth rate in Excel requires a basic **Exponential Formula** depending on its characteristics. However, plotting the bacteria culture values against time can also provide us with the required growth rate. In this article, we demonstrate ways to calculate bacterial growth rate using an **Exponential Formula** and **Excel Chart**.

Let’s say we have a dataset that showcases numbers in the growth of bacteria culture against time. Therefore, we want to calculate the growth rate of bacteria in those cultures.

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**2 Easy Ways to Calculate Bacterial Growth Rate in Excel**

**Method 1: Using an Exponential Formula to Calculate Bacterial Growth Rate in Excel**

Bacteria in cultures follow exponential growth. From experiments, we get the formula to calculate the growth rate. The **Growth Rate (µ)** formula is

` µ = ((log10 N - log10 N0) 2.303) / (t - t0)`

Here,

**N **= Number of Bacteria at **t** second

**N _{o }**= Number of Bacteria at

**t**second

_{o}**t **= a particular time in the growth period

**t _{o }**= starting time of bacteria culture

**Step 1:** Write the following formula in any blank cell (i.e., **E6**).

`= ((log10 N - log10 N0) 2.303) / (t - t0)`

**Step 2: **Press** ENTER** then Drag the **Fill Handle** to display the **Growth Rate** for **Bacteria Culture 1** as depicted in the image below.

**➤ **You can repeat **Steps 1** and **2** in order to bring out the **Growth Rate** for **Bacteria Culture 2 **similar to the picture below.

**Step 3: **After getting the **Growth Rate** percentages for **Bacteria Culture 1**, apply the **AVERAGE** function. The **AVERAGE** function calculates the average **Growth Rate** percentages out of those resultant percentages.

Type the below formula

`=AVERAGE(E5:E14)`

**➤ **Again, following **Step 3**, apply the **AVERAGE** formula to calculate the average **Growth Rate** of bacteria in **Culture 2**.

**Step 4: **You have to combine the two average **Growth Rate**s into an **Accumulated Average Growth Rate** using an **AVERAGE** formula. Use the formula written below

` =AVERAGE(E15:F15)`

**Step 5: **Hit the **ENTER** key and you get the **Accumulated Average Growth Rate** for the two **Bacteria Culture**s.

Calculating a bacteria culture **Growth Rate** requires experimental data and the formula must be compatible with the characteristics of that bacteria culture. However, we calculate the **Bacteria Growth Rate** using a typical empirical formula. You can use yours that is compatible with the bacteria characteristics.

🔁 To display the **Growth Rate** in percentages, you have to pre-formatted the cell in percentage **Category** from the **Format Cells** window.

**➤ **Select a range of cells then Press Keyboard shortcuts **CTRL+1** altogether to bring out the **Format Cells** window. Afterward, Select the **Number **section > Choose **Percentage **as **Category** > Assign the number of **Decimal Places** you want your data in.

Click **OK**.

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**Method 2: Using Chart Method to Display the Growth Rate**

In the previous method, we used an **Exponential Formula** to calculate the **Growth Rate** of a **Bacteria Culture**. Alternatively, we can use the dataset to display a **Curve Chart** from where we extract the **Exponential Formula**. Just by looking at the formula, we can easily find out the **Growth Rate** for each **Bacteria Culture**. The typical **Exponential Formula** of **Bacteria Culture **is

`y=b*emx`

In the formula,

**y **= yielding number of bacteria after **x** time.

**b **= Constant.

**m **= Bacteria Growth Rate

**Step 1:** Select the two columns (i.e., **Time** vs **Number for Bacteria Culture 1**). Then Go to the **Insert** tab > Select a **Chart Type** (shown in the screenshot) from **Scatter **options (from the **Charts** section).

**Step 2:** The **Chart** appears then **Right Click** on the **Chart**. The **Context Menu** pops up. From the **Context Menu**, Select **Select Data** from the options.

**Step 3:** The **Select Data** **Source** window appears. You can see there is an added data source already. You want to add the **bacteria culture 2** entries as another data source. In order to do so, Click on **Add** in the **Select Data Source** window.

**Step 4:** The **Edit Series** window opens up. Insert the respected data in **Series X** and** Y** values. Give the **Series** a Name (i.e., **Number of Bacteria (Culture 2)**).

Click **OK**.

**Step 5:** Clicking **OK** on the **Edit Series** dialog box takes you to the **Select Data Source** window again. In that window, we see there are two data sources. The two data sources mean you’ll have two **Curves** on the **Chart** of the two equations.

Click on **OK**.

**➤ **Similar to your expectations, you have two **Curves** on the **Chart**. One is there for **Culture 1** and the other for **Culture 2** as depicted in the following image.

**Step 6:** As we want to insert the formulas for each **Curve**. Click on any curve (i.e., **Orange Colored**) then **Right Click** on it.

The **Context Menu** appears. From the **Context Menu**, Select **Add Trendline**.

**Step 7:** The** Format Trendline** side common box appears. From the **Format Trendline **command box, Choose **Exponential **as **Trendline** **Options**. Afterward, **Scroll Down**.

**Step 8:** After Scrolling, you see an option saying **Display Formula on Chart**. Check the option as shown in the picture below.

**Step 9:** Go repeat **Step 6**, **7,** and** 8** for the** Blue Colored** curve and you get the exponential equations in the same colors for both **Curves**.

**➤ **If you want to add the **Chart** and **Axis** title, click on the big **PLUS Icon **button. A couple of options appear, Tick the **Axis** and **Chart Title** to display them on the chart.

**➤ **Assign suitable titles for the **Chart **and **Axis Title**. The entire chart looks similar to the image below.

You see the equations (i.e., **y=7566.7e ^{0.0605x} and y=7525.3e^{0.0594x}**) for both data sources. By comparing the equations to the typical

**Exponential Equation**(i.e.,

**Y=b*e**), you can say that the

^{mx}**Growth Rate**of the

**Bacteria Culture 1**and

**2**are

**0.605**or

**6.05%**and

**0.0594**or

**5.94%**respectively.

You can use as many data sources as you want. Then find the **Growth Rate** just by acquiring the equations.

**Related Content:**** How to Calculate Annual Growth Rate in Excel (3 Methods)**

**Conclusion**

In this article, we demonstrate ways to calculate the bacteria growth rate in Excel. We mainly use the empirical **Exponential Formula** to calculate the bacteria growth rate. We also use **Excel Chart **to provide us with the exponential formula. However, growth rates achieved by those two methods don’t match. This happens because we use an average formula to calculate the growth rate ignoring the phases of bacteria growth in cultures. But we use the most realistic approach by using an **Excel Chart** to find out the growth rate. Hope you find these methods easy to comprehend and use. Comment, if you have further inquiries or anything to add.