diff --git a/functional-tests/thin-calc-ref-counts b/functional-tests/thin-calc-ref-counts
new file mode 100644
index 0000000..1f5fd93
--- /dev/null
+++ b/functional-tests/thin-calc-ref-counts
@@ -0,0 +1,58 @@
+(import (chezscheme)
+        (bcache block-manager)
+	(fmt fmt)
+	(loops)
+        (persistent-data btree)
+	(thin metadata))
+
+(define (noop k v)
+  'nil)
+
+(define (mapping-top-level root)
+  (btree-open le64-vt root))
+
+(define (mapping-bottom-level root)
+  (btree-open le64-vt root))
+
+(define (mk-incrementer counts)
+ (lambda (i)
+  (vector-set! counts i (+ (vector-ref counts i) 1))))
+
+(define (bottom-level-walker cache inc-fn)
+ (lambda (key root)
+  (btree-each-and-count (mapping-bottom-level root) cache noop inc-fn)))
+
+(define (walk-top-level cache root counts)
+  (let ((inc-fn (mk-incrementer counts)))
+   (btree-each-and-count (mapping-top-level root)
+    			 cache
+			 (bottom-level-walker cache inc-fn)
+			 inc-fn)))
+
+(define (calc-ref-counts md-path)
+  (with-bcache (cache md-path (* 1 1024))
+    (let ((counts (make-vector (get-nr-blocks cache) 0)))
+     (with-block (b cache 0 (get-flags))
+      (let ((sb (block->superblock b)))
+	(walk-top-level cache
+	                (ftype-ref ThinSuperblock (data-mapping-root) sb)
+			counts)))
+
+     counts)))
+
+(define (print-counts counts)
+  (upto (i (vector-length counts))
+   (let ((rc (vector-ref counts i)))
+    (when (> rc 0)
+     (fmt #t i ": " (vector-ref counts i) nl)))))
+
+(define (usage)
+ (fmt #t "Usage: thin-calc-ref-counts <binary metadata>" nl)
+ (exit 1))
+
+(let ((args (cdr (command-line))))
+  (if (not (= (length args) 1))
+   (usage)
+   (let ((counts (calc-ref-counts (car args))))
+    (print-counts counts))))
+