How to Combine Line Charts in Tableau

Comparing multiple trends over time on a single visualization is a fantastic way to quickly spot relationships, correlations, and outliers in your data. Tableau makes this possible by allowing you to combine several line charts into one unified view. This guide will walk you through the primary methods for combining line charts, from plotting metrics with similar scales on a single axis to comparing measures of different magnitudes using a dual-axis chart.

Why Combine Line Charts?

Before jumping into the "how," let's quickly touch on the "why." Imagine you're analyzing marketing performance. You might want to see how an increase in website sessions impacts your conversion rate over the past quarter. Or, perhaps you want to compare the sales performance of three different product categories over the year.

Plotting these trend lines on a single chart makes it easy to see how they interact. Did a spike in traffic from a campaign lead to a corresponding jump in sales? Is Product A consistently outperforming Product B? Combining charts answers these questions visually, in a way that looking at separate charts or raw data never could.

Method 1: Combining Multiple Lines on a Single Axis

This is the most straightforward method and works best when the measures you're comparing are on a similar scale. For example, plotting the number of units sold for three different products, where the sales figures are all in the hundreds or thousands.

If you were to plot website sessions (in the thousands) and conversion rate (a small percentage like 3.5%) on the same axis, the conversion rate line would appear as a flat line near zero, making it impossible to analyze. We'll get to the solution for that in the next section.

Step-by-Step Instructions:

For this example, let's assume we have a dataset with monthly sales data for three regions: North, South, and East.

1. Set Up Your Time Dimension: Drag your date field (e.g., Order Date) to the Columns shelf. Right-click the pill and make sure it's a continuous date value, like MONTH(Order Date) with the green calendar icon. This creates your horizontal x-axis representing time.
2. Bring in Your First Measure: Drag your first measure (e.g., Sales) to the Rows shelf. You will see a single line chart representing total sales over time.
3. Use "Measure Values" and "Measure Names": The easiest way to get multiple lines on one chart is with Tableau’s generated fields. First, drag Measure Values from the Data pane onto the Rows shelf, replacing your Sales pill. By default, this may plot every measure in your dataset.
4. Filter Your Measures: Look for the Measure Values card that appeared on the left side of your screen below the Marks card. It will contain all the measures being plotted. Drag off any measures you don't want to see. For our example, we would keep North Sales, South Sales, and East Sales.
5. Add “Measure Names” to Color: To separate the single line into multiple colored lines - one for each measure - drag Measure Names from the Data pane onto the Color tile in the Marks card.

You now have a single, clean chart with three colored lines, each representing the sales for a different region over time. Tableau automatically creates a color legend for you, making it easy to see which line corresponds to which region.

Pro-Tip: When Your Data Structure is Vertical

What if your data is structured with a single "Sales" column and a separate "Region" column? This is an even easier and more common scenario.

• Drag your continuous Date field to Columns.
• Drag your Sales measure to Rows.
• Drag the Region dimension to the Color tile on the Marks card.

Tableau will automatically create separate lines for each member of the "Region" dimension (North, South, and East). This is often the most flexible way to build your visualizations.

Method 2: Creating a Dual-Axis Line Chart

The single-axis method falls apart when you need to compare measures with vastly different scales. Let’s say you want to compare your monthly Ad Spend (e.g., $50,000) with your Click-Through Rate (e.g., 2.1%). A dual-axis chart is the perfect solution, as it provides a separate vertical axis for each measure.

When to Use a Dual-Axis Chart:

• Different Scales: Comparing high-volume numbers (like Impressions) with small numbers (like Conversion Rate).
• Different Units: Comparing currency (e.g., Revenue) with percentages (e.g., Profit Margin) or whole numbers (e.g., Units Sold).

Step-by-Step Instructions:

1. Create the First Line Chart: As before, drag your Date field to the Columns shelf and your first measure (e.g., Ad Spend) to the Rows shelf.
2. Add the Second Measure: Drag your second measure (e.g., Click-Through Rate) to the right side of the visualization. As you drag, wait until you see a dashed green line appear along the right edge of the chart area, then release. This tells Tableau you want to create a new axis for this measure.
3. Enable Dual Axis: You now have two separate line charts stacked on top of each other. In the Rows shelf, you'll see two pills: one for Ad Spend and one for Click-Through Rate. Right-click the second pill (Click-Through Rate) and select Dual Axis from the dropdown menu.
4. Tidy Up the Marks Card: Your lines are now overlaid on the same chart space, but they might be displayed as different chart types (e.g., one line, one circle). Use the Marks card to fix this. At the top of the Marks card, you’ll see tabs for All, a tab for your first measure, and a tab for your second. Click the tab for the appropriate measure and change the mark type back to Line if needed. You can also adjust the colors for each line from their respective Marks cards.
5. Synchronize Your Axes (When Necessary): This is a crucial final step. If your two measures are on different scales but share the same unit (e.g., comparing sales of a high-volume product vs. a low-volume product in dollars), it's best to synchronize the axes so that the visual relationship is accurate. If your units are different (like dollars and percentages), do not synchronize them. To sync, right-click on the secondary y-axis (the one on the right) and select Synchronize Axis.

You now have a powerful dual-axis chart showing how your Ad Spend and Click-Through Rate trend together over time, each with its own properly scaled axis.

Combining a Line Chart with a Different Chart Type

The dual-axis technique isn't limited to two line charts. It’s also the primary way to overlay a line chart on top of another chart type, like a bar chart. This is great for showing a trend (the line) in the context of volume (the bars).

For example, you could show total sales per month as bars, with a line representing the profit ratio for those sales. This answers both "How much did we sell?" and "How profitable were those sales?" in one viz.

Quick Guide to a Bar-Line Combo Chart:

1. Create a bar chart showing Sales by Month. (Month on Columns, Sales on Rows).
2. Drag your second measure (e.g., Profit Ratio) to the Rows shelf, to the right of the Sales pill.
3. On the Marks shelf, you’ll now see tabs for both measures. Click the tab for Sales and ensure its mark type is set to Bar. Then click the tab for Profit Ratio and set its mark type to Line.
4. Right-click the Profit Ratio pill on the Rows shelf and select Dual Axis.
5. Adjust colors and formatting as needed for clarity.

Best Practices for Clear Visualizations

Combining charts is a great technique, but it can quickly lead to a cluttered and confusing mess if not handled with care. Here are a few tips to keep your charts clean and readable:

• Limit the Number of Lines: While you can technically plot many lines, a single chart becomes difficult to read after about four or five. If you need to compare more, consider breaking them into separate small multiple charts.
• Use Distinct Colors: Choose a color palette where each line is easily distinguishable. Avoid colors that are too similar, and be mindful of color blindness by using palettes with different levels of warmth and hue.
• Label Clearly: Make sure your axis titles are clear and include the units (e.g., "Sales ($ K)" and "Profit Ratio (%)"). A good title for the overall chart is also essential to give the viewer context.
• Leverage Tooltips: A cluttered chart hides details. Clean it up by putting extra information into the tooltip. When a user hovers over a data point, they can see the exact date, measure name, and value without it cluttering up the main view.

Final Thoughts

Combining line charts in Tableau, either through the Measure Values field for single-axis charts or the dual-axis feature for different scales, is a powerful way to visualize relationships in your data. Mastering these techniques will elevate your dashboards from simple data displays to compelling analytical stories.

While mastering techniques like dual-axis charts in Tableau is a valuable skill, it often involves several clicks, drags, and properties panels to get right. Sometimes you just want to see your data without becoming a BI tool expert. At Graphed, we built a tool that skips the manual setup. Instead of dragging pills onto shelves, you can just ask in plain English: "Show me a line chart comparing ad spend vs click-through rate from Google Ads this quarter." We instantly connect to your live data sources and build the dashboard for you, turning hours of report building into a 30-second conversation.