diff --git a/Makefile b/Makefile
index d174260..0f33271 100644
--- a/Makefile
+++ b/Makefile
@@ -19,6 +19,7 @@ run: $(ROM)
 
 a.out: main.o interrupt.o vectors.o platform.o apple2rom.cfg $(LIB)
 	$(CC65)/ld65 -C apple2rom.cfg -m main.map --dbgfile main.dbg interrupt.o vectors.o platform.o main.o $(LIB)
+	awk -f rom_usage.awk < main.map
 
 clean:
 	rm -f *.o *.lst a.out platform.s main.s $(LIB) tmp.lib
diff --git a/rom_usage.awk b/rom_usage.awk
new file mode 100644
index 0000000..bcc2f26
--- /dev/null
+++ b/rom_usage.awk
@@ -0,0 +1,14 @@
+# Pipe main.map into this to get ROM size info.
+
+/^CODE/ { code_start = ("0x" $2) + 0 }
+
+/^RODATA/ { rodata_end = ("0x" $3) + 0 }
+
+/^VECTORS/ { vectors_start = ("0x" $2) + 0 }
+
+END {
+    code = rodata_end - code_start + 1
+    all = vectors_start - code_start
+    printf "%d of %d ROM bytes (%d%%) used\n", code, all, code*100/all
+}
+