diff --git a/osbuild/util/parsing.py b/osbuild/util/parsing.py
new file mode 100644
index 00000000..303fbefa
--- /dev/null
+++ b/osbuild/util/parsing.py
@@ -0,0 +1,33 @@
+"""Helpers related to parsing"""
+
+import re
+from typing import Union
+
+
+def parse_size(s: str) -> Union[int, str]:
+    """Parse a size string into a number or 'unlimited'.
+
+    Supported suffixes: kB, kiB, MB, MiB, GB, GiB, TB, TiB
+    """
+    units = [
+        (r'^\s*(\d+)\s*kB$', 1000, 1),
+        (r'^\s*(\d+)\s*KiB$', 1024, 1),
+        (r'^\s*(\d+)\s*MB$', 1000, 2),
+        (r'^\s*(\d+)\s*MiB$', 1024, 2),
+        (r'^\s*(\d+)\s*GB$', 1000, 3),
+        (r'^\s*(\d+)\s*GiB$', 1024, 3),
+        (r'^\s*(\d+)\s*TB$', 1000, 4),
+        (r'^\s*(\d+)\s*TiB$', 1024, 4),
+        (r'^\s*(\d+)$', 1, 1),
+        (r'^unlimited$', "unlimited", 1),
+    ]
+
+    for pat, base, power in units:
+        m = re.fullmatch(pat, s)
+        if m:
+            if isinstance(base, int):
+                return int(m.group(1)) * base ** power
+            if base == "unlimited":
+                return "unlimited"
+
+    raise TypeError(f"invalid size value: '{s}'")
diff --git a/test/mod/test_util_parsing.py b/test/mod/test_util_parsing.py
new file mode 100644
index 00000000..faaa31a5
--- /dev/null
+++ b/test/mod/test_util_parsing.py
@@ -0,0 +1,39 @@
+"""Unit tests for osbuild.util.parsing"""
+
+import pytest
+
+from osbuild.util import parsing
+
+
+def test_parse_size():
+    cases = [
+        ("123", True, 123),
+        ("123 kB", True, 123000),
+        ("123 KiB", True, 123 * 1024),
+        ("123 MB", True, 123 * 1000 * 1000),
+        ("123 MiB", True, 123 * 1024 * 1024),
+        ("123 GB", True, 123 * 1000 * 1000 * 1000),
+        ("123 GiB", True, 123 * 1024 * 1024 * 1024),
+        ("123 TB", True, 123 * 1000 * 1000 * 1000 * 1000),
+        ("123 TiB", True, 123 * 1024 * 1024 * 1024 * 1024),
+        ("123kB", True, 123000),
+        ("123KiB", True, 123 * 1024),
+        (" 123", True, 123),
+        ("  123kB", True, 123000),
+        ("  123KiB", True, 123 * 1024),
+        ("unlimited", True, "unlimited"),
+        ("string", False, 0),
+        ("123 KB", False, 0),
+        ("123 mb", False, 0),
+        ("123 PB", False, 0),
+        ("123 PiB", False, 0),
+
+    ]
+
+    for s, success, num in cases:
+        if not success:
+            with pytest.raises(TypeError):
+                parsing.parse_size(s)
+        else:
+            res = parsing.parse_size(s)
+            assert res == num, f"{s} parsed as {res} (wanted {num})"