A table row was X columns wide, which is less than the column count established by the first row (Y).

HTML tables establish their column count based on the first row. When subsequent rows have fewer <td> or <th> cells than that initial row defines, the table structure becomes invalid. Browsers will typically render these tables by leaving blank space where the missing cells should be, but the underlying markup is malformed.

This matters for several important reasons. Screen readers and other assistive technologies rely on a consistent table structure to navigate cells and associate data with the correct headers. When cells are missing, users who depend on these tools may receive confusing or incorrect information. Additionally, inconsistent row widths can lead to unpredictable layout behavior across different browsers and make your table markup harder to maintain.

When counting columns, remember that the colspan attribute contributes to the total. A single <td colspan="3"> counts as three columns, not one. So if your first row has two <td> elements and one of them has colspan="2", the table is three columns wide, and every other row must also account for three columns.

How to Fix

There are several approaches depending on your intent:

1. Add the missing cells — If data was accidentally omitted, add the appropriate <td> or <th> elements to complete the row.
2. Use colspan — If a cell should intentionally span multiple columns, use the colspan attribute so the total column count matches.
3. Add empty cells — If a cell simply has no content, include an empty <td></td> to maintain the structure.

Examples

❌ Row with fewer columns than the first row

The first row establishes a 3-column table, but the second row only has 2 cells:

<table>
  <tr>
    <td>Name</td>
    <td>Role</td>
    <td>Department</td>
  </tr>
  <tr>
    <td>Alice</td>
    <td>Engineer</td>
  </tr>
</table>

✅ Fix by adding the missing cell

<table>
  <tr>
    <td>Name</td>
    <td>Role</td>
    <td>Department</td>
  </tr>
  <tr>
    <td>Alice</td>
    <td>Engineer</td>
    <td>Product</td>
  </tr>
</table>

✅ Fix by using colspan to span remaining columns

If the second row intentionally has fewer logical cells, use colspan so the total still matches:

<table>
  <tr>
    <td>Name</td>
    <td>Role</td>
    <td>Department</td>
  </tr>
  <tr>
    <td>Alice</td>
    <td colspan="2">Engineer — General</td>
  </tr>
</table>

✅ Fix by adding an empty cell

If there’s simply no data for that column, include an empty cell:

<table>
  <tr>
    <td>Name</td>
    <td>Role</td>
    <td>Department</td>
  </tr>
  <tr>
    <td>Alice</td>
    <td>Engineer</td>
    <td></td>
  </tr>
</table>

❌ Mismatch caused by colspan in the first row

Be careful when the first row uses colspan, as it increases the effective column count:

<table>
  <tr>
    <td colspan="2">Full Name</td>
    <td>Role</td>
  </tr>
  <tr>
    <td>Alice</td>
    <td>Engineer</td>
  </tr>
</table>

Here the first row spans 3 columns (2 + 1), but the second row only has 2 cells.

✅ Fix by matching the full column count

<table>
  <tr>
    <td colspan="2">Full Name</td>
    <td>Role</td>
  </tr>
  <tr>
    <td>Alice</td>
    <td>Smith</td>
    <td>Engineer</td>
  </tr>
</table>

Learn more:

MDN Reference

MDN: The table element

→

WHATWG Spec

HTML Spec: The table element

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