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---
comments: true
description: Learn how to validate your YOLOv8 model with precise metrics, easy-to-use tools, and custom settings for optimal performance.
keywords: Ultralytics, YOLOv8, model validation, machine learning, object detection, mAP metrics, Python API, CLI
---
# Model Validation with Ultralytics YOLO
<img width="1024" src="https://github.com/ultralytics/assets/raw/main/yolov8/banner-integrations.png" alt="Ultralytics YOLO ecosystem and integrations">
## Introduction
Validation is a critical step in the machine learning pipeline, allowing you to assess the quality of your trained models. Val mode in Ultralytics YOLOv8 provides a robust suite of tools and metrics for evaluating the performance of your object detection models. This guide serves as a complete resource for understanding how to effectively use the Val mode to ensure that your models are both accurate and reliable.
<p align="center">
<br>
<iframe loading="lazy" width="720" height="405" src="https://www.youtube.com/embed/j8uQc0qB91s?start=47"
title="YouTube video player" frameborder="0"
allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share"
allowfullscreen>
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<br>
<strong>Watch:</strong> Ultralytics Modes Tutorial: Validation
</p>
## Why Validate with Ultralytics YOLO?
Here's why using YOLOv8's Val mode is advantageous:
- **Precision:** Get accurate metrics like mAP50, mAP75, and mAP50-95 to comprehensively evaluate your model.
- **Convenience:** Utilize built-in features that remember training settings, simplifying the validation process.
- **Flexibility:** Validate your model with the same or different datasets and image sizes.
- **Hyperparameter Tuning:** Use validation metrics to fine-tune your model for better performance.
### Key Features of Val Mode
These are the notable functionalities offered by YOLOv8's Val mode:
- **Automated Settings:** Models remember their training configurations for straightforward validation.
- **Multi-Metric Support:** Evaluate your model based on a range of accuracy metrics.
- **CLI and Python API:** Choose from command-line interface or Python API based on your preference for validation.
- **Data Compatibility:** Works seamlessly with datasets used during the training phase as well as custom datasets.
!!! Tip "Tip"
* YOLOv8 models automatically remember their training settings, so you can validate a model at the same image size and on the original dataset easily with just `yolo val model=yolov8n.pt` or `model('yolov8n.pt').val()`
## Usage Examples
Validate trained YOLOv8n model accuracy on the COCO8 dataset. No argument need to passed as the `model` retains its training `data` and arguments as model attributes. See Arguments section below for a full list of export arguments.
!!! Example
=== "Python"
```python
from ultralytics import YOLO
# Load a model
model = YOLO("yolov8n.pt") # load an official model
model = YOLO("path/to/best.pt") # load a custom model
# Validate the model
metrics = model.val() # no arguments needed, dataset and settings remembered
metrics.box.map # map50-95
metrics.box.map50 # map50
metrics.box.map75 # map75
metrics.box.maps # a list contains map50-95 of each category
```
=== "CLI"
```bash
yolo detect val model=yolov8n.pt # val official model
yolo detect val model=path/to/best.pt # val custom model
```
## Arguments for YOLO Model Validation
When validating YOLO models, several arguments can be fine-tuned to optimize the evaluation process. These arguments control aspects such as input image size, batch processing, and performance thresholds. Below is a detailed breakdown of each argument to help you customize your validation settings effectively.
| Argument | Type | Default | Description |
| ------------- | ------- | ------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `data` | `str` | `None` | Specifies the path to the dataset configuration file (e.g., `coco8.yaml`). This file includes paths to validation data, class names, and number of classes. |
| `imgsz` | `int` | `640` | Defines the size of input images. All images are resized to this dimension before processing. |
| `batch` | `int` | `16` | Sets the number of images per batch. Use `-1` for AutoBatch, which automatically adjusts based on GPU memory availability. |
| `save_json` | `bool` | `False` | If `True`, saves the results to a JSON file for further analysis or integration with other tools. |
| `save_hybrid` | `bool` | `False` | If `True`, saves a hybrid version of labels that combines original annotations with additional model predictions. |
| `conf` | `float` | `0.001` | Sets the minimum confidence threshold for detections. Detections with confidence below this threshold are discarded. |
| `iou` | `float` | `0.6` | Sets the Intersection Over Union (IoU) threshold for Non-Maximum Suppression (NMS). Helps in reducing duplicate detections. |
| `max_det` | `int` | `300` | Limits the maximum number of detections per image. Useful in dense scenes to prevent excessive detections. |
| `half` | `bool` | `True` | Enables half-precision (FP16) computation, reducing memory usage and potentially increasing speed with minimal impact on accuracy. |
| `device` | `str` | `None` | Specifies the device for validation (`cpu`, `cuda:0`, etc.). Allows flexibility in utilizing CPU or GPU resources. |
| `dnn` | `bool` | `False` | If `True`, uses the OpenCV DNN module for ONNX model inference, offering an alternative to PyTorch inference methods. |
| `plots` | `bool` | `False` | When set to `True`, generates and saves plots of predictions versus ground truth for visual evaluation of the model's performance. |
| `rect` | `bool` | `False` | If `True`, uses rectangular inference for batching, reducing padding and potentially increasing speed and efficiency. |
| `split` | `str` | `val` | Determines the dataset split to use for validation (`val`, `test`, or `train`). Allows flexibility in choosing the data segment for performance evaluation. |
Each of these settings plays a vital role in the validation process, allowing for a customizable and efficient evaluation of YOLO models. Adjusting these parameters according to your specific needs and resources can help achieve the best balance between accuracy and performance.
### Example Validation with Arguments
The below examples showcase YOLO model validation with custom arguments in Python and CLI.
!!! Example
=== "Python"
```python
from ultralytics import YOLO
# Load a model
model = YOLO("yolov8n.pt")
# Customize validation settings
validation_results = model.val(data="coco8.yaml", imgsz=640, batch=16, conf=0.25, iou=0.6, device="0")
```
=== "CLI"
```bash
yolo val model=yolov8n.pt data=coco8.yaml imgsz=640 batch=16 conf=0.25 iou=0.6 device=0
```
## FAQ
### How do I validate my YOLOv8 model with Ultralytics?
To validate your YOLOv8 model, you can use the Val mode provided by Ultralytics. For example, using the Python API, you can load a model and run validation with:
```python
from ultralytics import YOLO
# Load a model
model = YOLO("yolov8n.pt")
# Validate the model
metrics = model.val()
print(metrics.box.map) # map50-95
```
Alternatively, you can use the command-line interface (CLI):
```bash
yolo val model=yolov8n.pt
```
For further customization, you can adjust various arguments like `imgsz`, `batch`, and `conf` in both Python and CLI modes. Check the [Arguments for YOLO Model Validation](#arguments-for-yolo-model-validation) section for the full list of parameters.
### What metrics can I get from YOLOv8 model validation?
YOLOv8 model validation provides several key metrics to assess model performance. These include:
- mAP50 (mean Average Precision at IoU threshold 0.5)
- mAP75 (mean Average Precision at IoU threshold 0.75)
- mAP50-95 (mean Average Precision across multiple IoU thresholds from 0.5 to 0.95)
Using the Python API, you can access these metrics as follows:
```python
metrics = model.val() # assumes `model` has been loaded
print(metrics.box.map) # mAP50-95
print(metrics.box.map50) # mAP50
print(metrics.box.map75) # mAP75
print(metrics.box.maps) # list of mAP50-95 for each category
```
For a complete performance evaluation, it's crucial to review all these metrics. For more details, refer to the [Key Features of Val Mode](#key-features-of-val-mode).
### What are the advantages of using Ultralytics YOLO for validation?
Using Ultralytics YOLO for validation provides several advantages:
- **Precision:** YOLOv8 offers accurate performance metrics including mAP50, mAP75, and mAP50-95.
- **Convenience:** The models remember their training settings, making validation straightforward.
- **Flexibility:** You can validate against the same or different datasets and image sizes.
- **Hyperparameter Tuning:** Validation metrics help in fine-tuning models for better performance.
These benefits ensure that your models are evaluated thoroughly and can be optimized for superior results. Learn more about these advantages in the [Why Validate with Ultralytics YOLO](#why-validate-with-ultralytics-yolo) section.
### Can I validate my YOLOv8 model using a custom dataset?
Yes, you can validate your YOLOv8 model using a custom dataset. Specify the `data` argument with the path to your dataset configuration file. This file should include paths to the validation data, class names, and other relevant details.
Example in Python:
```python
from ultralytics import YOLO
# Load a model
model = YOLO("yolov8n.pt")
# Validate with a custom dataset
metrics = model.val(data="path/to/your/custom_dataset.yaml")
print(metrics.box.map) # map50-95
```
Example using CLI:
```bash
yolo val model=yolov8n.pt data=path/to/your/custom_dataset.yaml
```
For more customizable options during validation, see the [Example Validation with Arguments](#example-validation-with-arguments) section.
### How do I save validation results to a JSON file in YOLOv8?
To save the validation results to a JSON file, you can set the `save_json` argument to `True` when running validation. This can be done in both the Python API and CLI.
Example in Python:
```python
from ultralytics import YOLO
# Load a model
model = YOLO("yolov8n.pt")
# Save validation results to JSON
metrics = model.val(save_json=True)
```
Example using CLI:
```bash
yolo val model=yolov8n.pt save_json=True
```
This functionality is particularly useful for further analysis or integration with other tools. Check the [Arguments for YOLO Model Validation](#arguments-for-yolo-model-validation) for more details.
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