How to Display 4 Products in One Row on Magento Homepage

in list.phtml under grid use below mention code

<?php // Grid Mode ?>

    <?php $_collectionSize = $_productCollection->count() ?>
   <?php $_columnCount = 5; ?>

Go to the homepage in the CMS -> Manage pages and add the following code snippet into the editor there

You could also use the same code to drill down into a specific category, by adding the category variable, e.g. be aware that here you have list_custom.phtml so you need to copy this there and just copy the list.phtml.

{{block type="catalog/product_list" name="home.catalog.product.list" alias="products_homepage" category_id="9" template="catalog/product/list_custom.phtml"}}

1) app\design\frontend\default\<your theme>\template\catalog\product copy list.phtml and save as list_custom.phtml

2) Now open list_custom.phtml and search for the following snippet. I have edited the $_columnCount = 4 as I want 4 products in one row and I have 4 products to show in the line if($i == 4) break;. So for you you will need the columntcount you want and then 36 as a break.

<?php // Grid Mode ?>
<?php $_collectionSize = $_productCollection->count() ?>
<?php //$_columnCount = $this->getColumnCount(); ?>
<?php $_columnCount = 4; ?>
<?php $i=0; foreach ($_productCollection as $_product): ?>
<?php 
$_productId = $_product->getId();?>
<?php if($i == 4) break; ?>
<?php if ($i++%$_columnCount==0): ?>
<ul class="products-grid row">