diff --git a/src/proto_alpha/lib_protocol/src/michelson_v1_gas.ml b/src/proto_alpha/lib_protocol/src/michelson_v1_gas.ml
index d59e95859..6f731bc2b 100644
--- a/src/proto_alpha/lib_protocol/src/michelson_v1_gas.ml
+++ b/src/proto_alpha/lib_protocol/src/michelson_v1_gas.ml
@@ -313,6 +313,8 @@ module Cost_of = struct
         | Concat_bytes -> alloc_cost 1
         | Slice_string -> alloc_cost 1
         | Slice_bytes -> alloc_cost 1
+        | String_size -> alloc_cost 1
+        | Bytes_size -> alloc_cost 1
         | Add_seconds_to_timestamp -> alloc_cost 1
         | Add_timestamp_to_seconds -> alloc_cost 1
         | Sub_timestamp_seconds -> alloc_cost 1
diff --git a/src/proto_alpha/lib_protocol/src/script_interpreter.ml b/src/proto_alpha/lib_protocol/src/script_interpreter.ml
index ca9a3acf5..864326a0e 100644
--- a/src/proto_alpha/lib_protocol/src/script_interpreter.ml
+++ b/src/proto_alpha/lib_protocol/src/script_interpreter.ml
@@ -429,6 +429,9 @@ let rec interp
             else
               Lwt.return (Gas.consume ctxt (Interp_costs.slice_string 0)) >>=? fun ctxt ->
               logged_return (Item (None, rest), ctxt)
+        | String_size, Item (s, rest) ->
+            Lwt.return (Gas.consume ctxt Interp_costs.push) >>=? fun ctxt ->
+            logged_return (Item (Script_int.(abs (of_int (String.length s))), rest), ctxt)
         (* bytes operations *)
         | Concat_bytes, Item (ss, rest) ->
             Lwt.return (Gas.consume ctxt (Interp_costs.concat_bytes ss)) >>=? fun ctxt ->
@@ -444,6 +447,9 @@ let rec interp
             else
               Lwt.return (Gas.consume ctxt (Interp_costs.slice_string 0)) >>=? fun ctxt ->
               logged_return (Item (None, rest), ctxt)
+        | Bytes_size, Item (s, rest) ->
+            Lwt.return (Gas.consume ctxt Interp_costs.push) >>=? fun ctxt ->
+            logged_return (Item (Script_int.(abs (of_int (MBytes.length s))), rest), ctxt)
         (* currency operations *)
         | Add_tez, Item (x, Item (y, rest)) ->
             Lwt.return (Gas.consume ctxt Interp_costs.int64_op) >>=? fun ctxt ->
diff --git a/src/proto_alpha/lib_protocol/src/script_ir_translator.ml b/src/proto_alpha/lib_protocol/src/script_ir_translator.ml
index d5b36d20d..6807c812b 100644
--- a/src/proto_alpha/lib_protocol/src/script_ir_translator.ml
+++ b/src/proto_alpha/lib_protocol/src/script_ir_translator.ml
@@ -157,8 +157,10 @@ let number_of_generated_growing_types : type b a. (b, a) instr -> int = function
   | Big_map_mem -> 0
   | Concat_string -> 0
   | Slice_string -> 0
+  | String_size -> 0
   | Concat_bytes -> 0
   | Slice_bytes -> 0
+  | Bytes_size -> 0
   | Add_seconds_to_timestamp -> 0
   | Add_timestamp_to_seconds -> 0
   | Sub_timestamp_seconds -> 0
@@ -2126,6 +2128,10 @@ and parse_instr
           loc annot >>=? fun annot ->
         typed ctxt loc Slice_string
           (Item_t (Option_t ((String_t tname, None), None, None), rest, annot))
+    | Prim (loc, I_SIZE, [], annot),
+      Item_t (String_t _, rest, _) ->
+        parse_var_annot loc annot >>=? fun annot ->
+        typed ctxt loc String_size (Item_t (Nat_t None, rest, annot))
     (* bytes operations *)
     | Prim (loc, I_CONCAT, [], annot),
       Item_t (List_t (Bytes_t tname, _), rest, list_annot) ->
@@ -2139,6 +2145,10 @@ and parse_instr
           loc annot >>=? fun annot ->
         typed ctxt loc Slice_bytes
           (Item_t (Option_t ((Bytes_t tname, None), None, None), rest, annot))
+    | Prim (loc, I_SIZE, [], annot),
+      Item_t (Bytes_t _, rest, _) ->
+        parse_var_annot loc annot >>=? fun annot ->
+        typed ctxt loc Bytes_size (Item_t (Nat_t None, rest, annot))
     (* currency operations *)
     | Prim (loc, I_ADD, [], annot),
       Item_t (Mutez_t tn1, Item_t (Mutez_t tn2, rest, _), _) ->
@@ -2671,7 +2681,7 @@ and parse_instr
         Lwt.return @@ serialize_ty_for_error ctxt ta >>=? fun (ta, ctxt) ->
         Lwt.return @@ serialize_ty_for_error ctxt tb >>=? fun (tb, _ctxt) ->
         fail (Undefined_binop (loc, name, ta, tb))
-    | Prim (loc, (I_NEG | I_ABS | I_NOT | I_CONCAT
+    | Prim (loc, (I_NEG | I_ABS | I_NOT | I_CONCAT | I_SIZE
                  | I_EQ | I_NEQ | I_LT | I_GT | I_LE | I_GE as name),
             [], _),
       Item_t (t, _, _) ->
diff --git a/src/proto_alpha/lib_protocol/src/script_typed_ir.ml b/src/proto_alpha/lib_protocol/src/script_typed_ir.ml
index ad3f8c0eb..98889455e 100644
--- a/src/proto_alpha/lib_protocol/src/script_typed_ir.ml
+++ b/src/proto_alpha/lib_protocol/src/script_typed_ir.ml
@@ -206,11 +206,15 @@ and ('bef, 'aft) instr =
       (string list * 'rest, string * 'rest) instr
   | Slice_string :
       (n num * (n num * (string * 'rest)), string option * 'rest) instr
+  | String_size :
+      (string * 'rest, n num * 'rest) instr
   (* bytes operations *)
   | Concat_bytes :
       (MBytes.t list * 'rest, MBytes.t * 'rest) instr
   | Slice_bytes :
       (n num * (n num * (MBytes.t * 'rest)), MBytes.t option * 'rest) instr
+  | Bytes_size :
+      (MBytes.t * 'rest, n num * 'rest) instr
   (* timestamp operations *)
   | Add_seconds_to_timestamp :
       (z num * (Script_timestamp.t * 'rest),