diff --git a/lib/moi/util/format.elv b/lib/moi/util/format.elv
index 65464f6..bc5d2e5 100644
--- a/lib/moi/util/format.elv
+++ b/lib/moi/util/format.elv
@@ -177,3 +177,27 @@ fn list {|&with-header=$true &csep=' ' &hsep='-' &recompute=$true props data|
     echo (line &sep=$csep $props $d)
   } $data
 }
+
+fn size {|size|
+  var u = 0
+  var m = [
+    &10=Kio
+    &20=Mio
+    &30=Gio
+  ]
+  while (< $u 30) {
+    var p = (math:pow 2 (+ $u 10))
+    if (< $size $p) {
+      break
+    }
+    set u = (to-string (+ $u 10))
+  }
+  if (== $u 0) {
+    put $size
+  } else {
+    var p = (math:pow 2 (+ $u 10))
+    var e = (/ $size $p)
+    printf '%.1f%s' $e $m[$u]
+  }
+
+}