---
title: "Bounding boxes in PDF annotations guide | Nutrient .NET SDK"
canonical_url: "https://www.nutrient.io/guides/dotnet/annotations/introduction-to-annotations/bounding-boxes/"
md_url: "https://www.nutrient.io/guides/dotnet/annotations/introduction-to-annotations/bounding-boxes.md"
last_updated: "2026-05-21T17:12:02.199Z"
description: "Learn how bounding boxes define size and location in PDF annotations, enhancing interactivity and information delivery."
---

# Understanding bounding boxes in PDF annotations

Bounding boxes in PDF annotations are used to define the location and size of an annotation within a PDF document. PDF annotations are visual elements that can be added to a PDF page to provide additional information or interactivity. Bounding boxes are rectangular regions that enclose the annotated content.

A bounding box is represented by four values: the X coordinate of the left edge, the Y coordinate of the top edge, the width, and the height. These values define the position and dimensions of the bounding box in the coordinate system of the PDF page.

The coordinate system used is based on a grid where the origin (0, 0) is defined by the [`SetOrigin` method](https://www.nutrient.io/api/gdpicture/GdPicture.NET.14.API~GdPicture14.GdPicturePDF~SetOrigin.html). It uses a member of the [`PdfOrigin` enumeration](https://www.nutrient.io/api/gdpicture/GdPicture.NET.14.API~GdPicture14.PdfOrigin.html) as its parameter. The direction of the X and Y axes changes depending on which member of the `PdfOrigin` enumeration is used. However, the axes are always directed toward the PDF page.

The measurement unit used to specify the bounding box is defined using the [`SetMeasurementUnit` method](https://www.nutrient.io/api/gdpicture/GdPicture.NET.14.API~GdPicture14.GdPicturePDF~SetMeasurementUnit.html). It uses a member of the [`PdfMeasurementUnit` enumeration](https://www.nutrient.io/api/gdpicture/GdPicture.NET.14.API~GdPicture14.PdfMeasurementUnit.html) as its parameter.
---

## Related pages

- [Understanding PDF and XMP annotations for collaboration](/guides/dotnet/annotations/introduction-to-annotations/what-are-annotations-pdf.md)
- [What are XMP annotations?](/guides/dotnet/annotations/introduction-to-annotations/what-are-annotations-xmp.md)
- [Understanding common types of PDF annotations](/guides/dotnet/annotations/introduction-to-annotations/annotation-types.md)