diff --git a/sum-sizes b/sum-sizes
new file mode 100755
index 0000000..0aba891
--- /dev/null
+++ b/sum-sizes
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+#!/usr/bin/env python3
+# Read file sizes from stdin, print sum on stdout
+# Accepted formats on stdin:
+# - '1.2 MB', interpreted as 1200000 bytes
+# - '1.2 MiB', interpreted as 1.20 * 1024 * 1024 = 1258291.2 bytes
+# - '1.2M', interpreted as MiB
+# - '123', interpreted as 123 bytes
+# Known units: B; kB, MB, GB, TB, PB, EB; KiB, MiB, GiB, TiB, PiB, EiB; K, M, G, T, P, E
+# In all cases, whitespace is optional, can be any width, and may contain tabs. Leading and trailing whitespace is also permitted.
+# All numbers are cast to an integer before summation.
+# Output is by default formatted as IEC (i.e. KiB, MiB, etc.).
+
+import math
+import re
+import sys
+
+
+units = {
+	'B': 1,
+
+	# SI prefixes
+	'kB': 1000,
+	'MB': 1000**2,
+	'GB': 1000**3,
+	'TB': 1000**4,
+	'PB': 1000**5,
+	'EB': 1000**6,
+
+	# IEC
+	'KiB': 1024,
+	'MiB': 1024**2,
+	'GiB': 1024**3,
+	'TiB': 1024**4,
+	'PiB': 1024**5,
+	'EiB': 1024**6,
+
+	# Short IEC
+	'K': 1024,
+	'M': 1024**2,
+	'G': 1024**3,
+	'T': 1024**4,
+	'P': 1024**5,
+	'E': 1024**6,
+}
+sum = 0
+for line in sys.stdin:
+	origLine = line
+	line = re.sub(r'\s+', '', line.strip())
+	line = re.sub(r'([a-zA-Z])', r' \1', line, count = 1)
+	if ' ' in line:
+		number, unit = line.split(' ', 1)
+	else:
+		number = line
+		unit = 'B'
+	if unit not in units:
+		print(f'Skipping line with unknown unit: {origLine}', file = sys.stderr)
+		continue
+	try:
+		number = float(number)
+	except ValueError as e:
+		print(f'Skipping line with unparseable number: {origLine}', file = sys.stderr)
+		continue
+	if number.is_integer():
+		number = int(number)
+	sum += int(number * units[unit])
+
+# Special case because log(0) is kinda bad...
+if sum == 0:
+	print('0 B')
+	sys.exit(0)
+
+log = int(math.log(sum if sum > 0 else -sum, 1024))
+unit = ['B', 'KiB', 'MiB', 'GiB', 'TiB', 'PiB', 'EiB'][log]
+if unit == 'B':
+	print(f'{sum} {unit}')
+else:
+	print(f'{sum / 1024**log :.2f} {unit}')