---
title: "How to use percentages and ratios in Custom Data Import"
slug: "how-to-use-percentages-and-ratios-in-custom-data-import"
description: "Learn how to create custom fields for accurate ratio data like click-through rate and cost per action using Custom Data Import for better insights."
updated: 2025-09-01T11:14:02Z
published: 2025-09-01T11:14:02Z
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.supermetrics.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How to use percentages and ratios in Custom Data Import

Sometimes reports you are looking to import contain ratio data such as click-through rate (CTR) or cost per action (CPA). As a general rule, we don't recommend using ratio fields directly from your import as the data may give inaccurate results when aggregated to a different granularity than what they were in the original file.

Instead, we suggest creating a custom field for these percentages based on the raw source values. First, you’ll need to import the raw data using Custom Data Import and then you'll create the custom fields for percentage or ratio data. For example, click-through rate = Clicks / Impressions or cost per action = Spend / Actions.

## Instructions

1. [Import your data using Custom Data Import as instructed in this guide](/v1/docs/how-to-configure-a-data-import-for-custom-data-import). Make sure to exclude the calculated data from the import.
2. On the [Supermetrics Hub](https://hub.supermetrics.com/), go to **Custom data import** under **Connect**.
3. Click **New custom field**.
4. Select metric and click **Next**.This selection is based on the aspect of the data you aim to manipulate. For instance, if you're looking to calculate Click-Through Rate (CTR), you'd be working with metrics ('Clicks' and 'Impressions').
5. Select the Custom Data Import data source and click **Next**.
6. In the **Select report type** dropdown, select the data import you want to create the custom field for.
7. Select **Function** as your transformation type.This selection enables you to manipulate your selected data using a variety of mathematical or textual operations.
8. From the list of available functions, select the one that best suits your needs. For percentages and ratios, select Divide.
9. Then, specify the **Divide** (the number to be divided) and **by** (the number to divide by) fields.
10. After configuring your function, click **Next**.
11. Give a name for your custom field.
12. Click **Create custom field**.
13. In your data destination, select the Custom Data Import connector, the data import you created the custom field for, and the custom field you just created.

Learn more about [how to use custom fields in your reporting](/v1/docs/how-to-use-custom-fields-in-your-reporting).