If you're buying fabric without a specific project in mind, it's a good idea to buy a little more than you think you'll need. The amount of fabric you should buy depends on a few factors, including the width of the fabric, the type of fabric, and your own personal preferences. Here are some general guidelines to follow:

Width of the fabric: Most fabric comes in standard widths, such as 45" (112cm as with most of our quilting fabrics), 54" (137cm), or 60" (150cm). The wider the fabric, the less you'll need to buy to get a certain length. For example, if you want to buy 2m of fabric, you'll need to buy more of a 45" wide fabric than you would of a 60" wide fabric.

Type of fabric: Different types of fabric have different weights and densities, which can affect how much you need. For example, a lightweight cotton fabric will require less yardage than a heavyweight wool fabric.

Personal preferences: If you like to have extra fabric on hand for making samples or experimenting with new techniques, you may want to buy more than you need. On the other hand, if you're on a tight budget or don't have a lot of storage space, you may want to buy less.

As a general rule of thumb, buying 3-4m of fabric should be enough for most sewing projects, unless the project specifically requires more or less. This will give you enough fabric to make a dress, a skirt, or a blouse, and still have some left over for smaller projects or experimentation. However, if you're buying a fabric that is more expensive or has a directional print or pattern, you may want to buy more to make sure you have enough for any future projects.