For one file, use os.path.getsize(path) or Path(path).stat().st_size; both return a logical size in bytes. For a folder’s contents, walk its files and add their sizes. A directory’s own st_size is not the total size of everything inside it.
Get the size of one file
The simplest option is os.path.getsize(). Give it a file path, and it returns the file’s size as an integer number of bytes. For example:
import os
size_bytes = os.path.getsize("report.pdf")
print(size_bytes)The equivalent using pathlib is to call stat() and read its st_size field:
from pathlib import Path
size_bytes = Path("report.pdf").stat().st_size
print(size_bytes)These methods are for a path that identifies a file. They raise an OSError if the path is missing or cannot be accessed, so decide whether your program should stop, report the problem, or handle it and continue.
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Use the value as bytes
Keep the original integer for comparisons, limits, and calculations. Convert to a human-readable unit only when displaying it. The following helper uses binary units, where each step is 1,024 bytes:
def human_bytes(n: int) -> str:
units = ["B", "KiB", "MiB", "GiB", "TiB"]
value = float(n)
for unit in units:
if value < 1024 or unit == units[-1]:
return f"{value:.1f} {unit}"
value /= 1024
print(human_bytes(size_bytes))For example, this helper will display 1,048,576 bytes as 1.0 MiB. It formats the number; it does not change the underlying byte count.
Calculate a folder’s total size recursively
A folder total is the sum of the sizes of the files you choose to include beneath that folder. Python’s os.walk() is a straightforward way to visit the tree. This version sums readable files and skips paths that raise OSError:
import os
def folder_size(path: str) -> int:
total = 0
for root, dirs, files in os.walk(path):
for name in files:
file_path = os.path.join(root, name)
try:
total += os.path.getsize(file_path)
except OSError:
# Replace with logging or re-raise if skipped files matter.
pass
return total
print(folder_size("my_folder"))The return value is an integer byte count. The error handler is a policy choice, not a guarantee that the result includes every file: if a file disappears or access is denied during traversal, this example skips it. For backups, audits, or billing calculations, you may prefer to record skipped paths or fail rather than silently return a partial total.
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os.walk() provides a mutable dirs list for each visited directory. Remove entries from it to prune subtrees before they are traversed. This example excludes every directory named __pycache__:
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import os
def folder_size_without_pycache(path: str) -> int:
total = 0
for root, dirs, files in os.walk(path):
dirs[:] = [name for name in dirs if name != "__pycache__"]
for name in files:
try:
total += os.path.getsize(os.path.join(root, name))
except OSError:
pass
return totalPruning matters when excluded folders may be large: it avoids visiting their contents, rather than merely leaving their file sizes out of the final sum.
Use pathlib on Python 3.12 and later
Path.walk() offers a pathlib-style traversal, but it requires Python 3.12 or later. The following sums file sizes under a directory:
from pathlib import Path
def folder_size(path: Path) -> int:
total = 0
for root, dirs, files in path.walk():
for name in files:
try:
total += (root / name).stat().st_size
except OSError:
pass
return total
print(folder_size(Path("my_folder")))As with the os.walk() version, remove excluded names from dirs if you want to prune folders. For example, add dirs[:] = [name for name in dirs if name != "__pycache__"] inside the loop before processing files. If you need to support Python versions before 3.12, use os.walk() or another available traversal method instead.
Choose the traversal and symlink policy
The right implementation depends on which paths count toward your total, how you want errors handled, and which Python version you support.
| Approach | When it fits | Important behavior |
|---|---|---|
os.path.getsize() |
Checking one path | Returns bytes; raises OSError for missing or inaccessible paths. |
Path.stat().st_size |
Checking one path with pathlib | Returns the stat result’s size; stat() follows a symlink. |
os.walk() |
Recursive folder totals and broad Python-version compatibility | Does not descend into directory symlinks by default. Setting followlinks=True can loop if links point back to an ancestor. |
Path.walk() |
Recursive traversal with pathlib on Python 3.12+ | Use dirs to prune subtrees; decide how to handle per-file errors and links. |
os.scandir() |
Directory iteration where entry metadata is useful | DirEntry provides path and stat methods; stat calls can raise OSError. |
Decide whether links count
For a file symlink, Path.stat() follows the link and reports the target’s size. Path.lstat() instead reports information about the link itself. Be explicit about which meaning you need; otherwise, a total can include target data when you expected only the link entry.
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For directory links, the default os.walk() behavior is not to descend into them. Turning on followlinks=True changes what the traversal includes, and can cause infinite recursion when a link points to one of its parent directories. Only enable it when following directory links is intentional and your traversal accounts for cycles. The sample folder-total function does not follow directory symlinks.
Use scandir when entry checks are useful
os.walk() already uses os.scandir() internally. If you need direct access to directory entries—for example, to inspect entry types while iterating—you can use DirEntry methods. This example counts regular files in each directory without following file symlinks:
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import os
def folder_size(path: str) -> int:
total = 0
for root, dirs, files in os.walk(path):
with os.scandir(root) as entries:
for entry in entries:
try:
if entry.is_file(follow_symlinks=False):
total += entry.stat(follow_symlinks=False).st_size
except OSError:
# Choose whether to log, skip, or re-raise.
pass
return totalThis illustrates entry-level type and metadata checks; it also calls os.walk() to enumerate directories. For a simple recursive sum, the earlier os.walk() version is easier to read. Any stat operation may fail while the tree is changing or access is restricted.
Understand what the total measures
These examples add logical file sizes—the st_size values—in bytes. That is not necessarily the amount of physical storage allocated on a filesystem. Sparse or compressed files can have a logical size that differs from their allocated disk blocks.
A folder-content total is also different from filesystem capacity. To ask how much space the filesystem has in total, uses, or has free, call shutil.disk_usage():
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import shutil
usage = shutil.disk_usage("my_folder")
print("total:", usage.total)
print("used:", usage.used)
print("free:", usage.free)Those named fields are capacity figures in bytes for the filesystem containing the supplied path. They do not tell you how many logical bytes are inside that particular folder.
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Handle errors and changing directories
A recursive size calculation is a traversal-time estimate, not a transactionally consistent snapshot. Files can be created, removed, resized, or made inaccessible while your code walks the tree. A file that vanishes between discovery and stat, or a permissions change, can cause getsize(), Path.stat(), or DirEntry.stat() to raise OSError.
Pick an error policy that fits the use case:
- Fail fast: let the exception propagate when a partial answer would be misleading.
- Report and continue: catch
OSError, record the path and error, then include the skipped-path count in the result. - Skip quietly: suitable only when omissions are acceptable and the total is clearly understood as best-effort.
For security-sensitive or audit work, also consider that symlink targets and file contents can change during traversal. A simple walk-and-sum does not lock the tree or make the result atomic.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot common size mismatches
A directory reports only a small number
That is the directory entry’s own metadata size, not a recursive total. Walk the descendants and sum file sizes to measure contents.
The result is smaller than the space used on disk
You may be comparing logical file bytes with allocated storage, which can differ for sparse or compressed files. You may also be excluding inaccessible files or directory symlinks. Check the traversal and error policy before interpreting the difference.
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The function raises FileNotFoundError or PermissionError
Both are forms of OSError. Confirm that the path exists and that the process can access it. If the tree may change during the walk, choose whether that condition should stop the calculation or be logged and skipped.
The total seems unexpectedly large
Check whether file symlinks are being followed, whether the same target is reachable through more than one path, and whether your traversal follows directory symlinks. Avoid enabling followlinks=True without a cycle policy.
The pathlib folder example does not run
Path.walk() is available in Python 3.12 and later. Check your interpreter version; for earlier versions, use os.walk().
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