diff --git a/tools/free_space.awk b/tools/free_space.awk
index 1f2b04415..d9096a0d3 100755
--- a/tools/free_space.awk
+++ b/tools/free_space.awk
@@ -1,13 +1,70 @@
-#!/usr/bin/awk -f
+#!/usr/bin/gawk -f
 
-# Usage: tools/free_space.awk pokecrystal.map
+# Usage:  tools/free_space.awk [BANK=<bank_spec>] pokecrystal.map
+
+# The BANK argument allows printing free space in one, all, or none of the ROM's banks.
+# Valid arguments are numbers (in decimal "42" or hexadecimal "0x2a"), "all" or "none".
+# If not specified, defaults to "none".
+# The `BANK` argument MUST be before the map file name, otherwise it has no effect!
+# Yes:  tools/free_space.awk BANK=all pokecrystal.map
+# No:   tools/free_space.awk pokecrystal.map BANK=42
+
+# Copyright (c) 2020, Eldred Habert.
+# SPDX-License-Identifier: MIT
 
 BEGIN {
-	total = free = 16384 * 128
+	nb_banks = 0
+	free = 0
+	rom_bank = 0 # Safety net for malformed files
+
+	# Default settings
+	# Variables assigned via the command-line (except through `-v`) are *after* `BEGIN`
+	BANK="none"
 }
-/^  SECTION: \$[0-7]/ {
-	free -= strtonum("0x" substr($3, 3))
+
+# Only accept ROM banks, ignore everything else
+toupper($0) ~ /^[ \t]*ROM[0X][ \t]+BANK[ \t]+#/ {
+	nb_banks++
+	rom_bank = 1
+	split($0, fields, /[ \t]/)
+	bank_num = strtonum(substr(fields[3], 2))
 }
+
+function register_bank(amount) {
+	free += amount
+	rom_bank = 0 # Reject upcoming banks by default
+
+	if (BANK ~ /all/ || BANK == bank_num) {
+		printf "Bank %3d: %5d/16384 (%.2f%%)\n", bank_num, amount, amount * 100 / 16384
+	}
+}
+
+rom_bank && toupper($0) ~ /^[ \t]*EMPTY/ {
+	# Empty bank
+	register_bank(16384)
+}
+rom_bank && toupper($0) ~ /^[ \t]*SLACK:[ \t]/ {
+	if ($2 ~ /\$[0-9A-F]+/) {
+		register_bank(strtonum("0x" substr($2, 2)))
+	} else {
+		printf "Malformed slack line? \"%s\" does not start with '$'\n", $2
+	}
+}
+
 END {
-	printf "Free space: %d/%d (%.2f%%)\n", free, total, free * 100 / total
+	# Determine number of banks, by rounding to upper power of 2
+	total_banks = 2 # Smallest size is 2 banks
+	while (total_banks < nb_banks) {
+		total_banks *= 2
+	}
+
+	# RGBLINK omits "trailing" ROM banks, so fake them
+	bank_num = nb_banks
+	while (bank_num < total_banks) {
+		register_bank(16384)
+		bank_num++
+	}
+
+	total = total_banks * 16384
+	printf "Free space: %5d/%5d (%.2f%%)\n", free, total, free * 100 / total
 }