PythonBeginner.help

Python Folder Size Calculator Example

Build a simple Python script that calculates the total size of files inside a folder. This example helps beginners practice working with file paths, loops, and the os module.

If you want the shortest working version first, start here:

import os

folder_path = "."
total_size = 0

for name in os.listdir(folder_path):
    path = os.path.join(folder_path, name)
    if os.path.isfile(path):
        total_size += os.path.getsize(path)

print(f"Total size: {total_size} bytes")

This quick version adds the size of files in one folder only. A later section expands it to include subfolders.

What this example does #

This example shows how to:

  • Calculate the total size of files in a folder
  • Combine os.listdir(), os.path.join(), and os.path.getsize()
  • Understand how file system paths work in Python
  • Solve one practical task with a small script

This is a good beginner project because it uses a loop, file paths, and built-in standard library tools in one place.

What you need to know first #

Before reading the code, it helps to understand a few basics:

  • A folder can contain files and subfolders
  • A file path tells Python where a file or folder is
  • The os module gives you tools for working with files and folders
  • A loop lets you process items one by one

If file paths still feel confusing, see working with file paths in Python.

Simple version: total size of files in one folder #

This version checks one folder only. It does not go inside subfolders.

import os

folder_path = "."

total_size = 0

for name in os.listdir(folder_path):
    path = os.path.join(folder_path, name)

    if os.path.isfile(path):
        total_size += os.path.getsize(path)

print(f"Total size: {total_size} bytes")

How it works #

  • os.listdir(folder_path) gets the names of items in the folder
  • os.path.join(folder_path, name) builds the full path
  • os.path.isfile(path) checks whether the item is a file
  • os.path.getsize(path) gets the file size in bytes

Why os.path.join() matters #

Do not build paths by hand with string addition. This can break on different operating systems.

Good:

path = os.path.join(folder_path, name)

Less reliable:

path = folder_path + "/" + name

If you want a deeper explanation, see os.path.join() explained.

Example output #

Total size: 15432 bytes

Recursive version: include subfolders #

The basic version only counts files in the current folder. If you want the total size of a folder and everything inside it, including subfolders, use os.walk().

import os

folder_path = "."

total_size = 0

for root, dirs, files in os.walk(folder_path):
    for name in files:
        path = os.path.join(root, name)
        total_size += os.path.getsize(path)

print(f"Total size: {total_size} bytes")

How this version works #

  • os.walk(folder_path) goes through the folder and all subfolders
  • root is the current folder being processed
  • files is a list of file names in that folder
  • Each file path is built with os.path.join(root, name)
  • The script adds the size of every file it finds

This version is usually more useful for real folder size checks.

Show the size in a readable format #

File sizes in bytes are correct, but they are not always easy to read. You can add a helper function to show sizes in KB, MB, or GB.

import os

def format_size(size_in_bytes):
    units = ["bytes", "KB", "MB", "GB", "TB"]
    size = float(size_in_bytes)

    for unit in units:
        if size < 1024 or unit == units[-1]:
            return f"{size:.2f} {unit}"
        size /= 1024

folder_path = "."
total_size = 0

for root, dirs, files in os.walk(folder_path):
    for name in files:
        path = os.path.join(root, name)
        total_size += os.path.getsize(path)

print(f"Folder: {folder_path}")
print(f"Total size: {format_size(total_size)}")

Example output #

Folder: .
Total size: 2.45 MB

The helper function keeps the conversion logic separate from the main loop, which makes the script easier to read.

Common problems and how to avoid them #

Here are the most common reasons this script does not work as expected:

  • The folder path is wrong
  • The script counts only the current folder, not subfolders
  • File paths are built incorrectly
  • A permission error blocks access to some files
  • The output is shown only in bytes when you expected KB or MB

1. The folder path does not exist #

If the path is wrong, Python may raise an error such as FileNotFoundError.

Check the path first:

import os

folder_path = "my_folder"
print(folder_path)
print(os.path.exists(folder_path))

If False is printed, the path is not valid from the script’s current location.

For help with this error, see how to fix FileNotFoundError: Errno 2 No such file or directory.

2. You expected subfolders to be included #

This is a very common mistake. The os.listdir() version only checks one folder level.

If you want subfolders too, switch to os.walk().

3. Paths are built incorrectly #

Always combine paths with os.path.join().

You can debug by printing the path:

import os

folder_path = "."
for name in os.listdir(folder_path):
    path = os.path.join(folder_path, name)
    print(path)

You can also learn more in how to list files in a directory in Python and os.listdir() explained.

4. A folder is passed to getsize() #

os.path.getsize() works on paths, but in this kind of script you usually want file sizes only.

Check with os.path.isfile(path) first:

import os

folder_path = "."

for name in os.listdir(folder_path):
    path = os.path.join(folder_path, name)
    print(os.path.isfile(path))

5. Permission errors stop the script #

Some files may not be accessible. In that case, you may get PermissionError.

A simple way to make the script more robust is to skip files that cannot be read:

import os

folder_path = "."
total_size = 0

for root, dirs, files in os.walk(folder_path):
    for name in files:
        path = os.path.join(root, name)
        try:
            total_size += os.path.getsize(path)
        except PermissionError:
            print(f"Skipped: {path}")

print(f"Total size: {total_size} bytes")

If this happens often, read how to fix PermissionError: Errno 13 Permission denied.

Helpful debugging prints #

When the result looks wrong, these simple checks can help:

print(folder_path)
print(os.path.exists(folder_path))
print(os.path.isfile(path))
print(os.path.getsize(path))
print(root, files)

Ways to improve the script #

Once the basic version works, you can extend it in useful ways:

  • Ask the user for a folder path with input()
  • Skip hidden files if needed
  • Show the largest files in the folder
  • Print separate totals for each subfolder

Here is one simple improvement that lets the user choose the folder:

import os

folder_path = input("Enter a folder path: ")
total_size = 0

for root, dirs, files in os.walk(folder_path):
    for name in files:
        path = os.path.join(root, name)
        total_size += os.path.getsize(path)

print(f"Total size: {total_size} bytes")

You could also combine this with the readable size function from the earlier section.

FAQ #

Does this script include subfolders? #

The basic version does not. Use a recursive version with os.walk() to include subfolders.

Why am I getting FileNotFoundError? #

The path may be wrong, or the current working directory may not be what you expect.

Why is the size shown in bytes? #

os.path.getsize() returns bytes. You can convert that value to KB, MB, or GB.

Can I calculate folder size with pathlib instead of os? #

Yes, but this example keeps things simple by using os tools that many beginners learn first.

See also #

Try extending this example next by adding subfolder support, readable file sizes, or a report that shows the largest files.

Press Esc to close