diff --git a/API-Reference.md b/API-Reference.md
index b798b80..dcc129b 100644
--- a/API-Reference.md
+++ b/API-Reference.md
@@ -821,6 +821,47 @@ const char* value2 = object.get<const char*>("toto"); // returns NULL
 ```
 
 
+### JsonObject::measureLength()
+
+##### Description
+
+Gets the length of string produced by `JsonObject::printTo()`.
+
+This can be very handy to fill the `Content-Length` of an HTTP request or response.
+
+##### Return value
+
+The number of characters in the JSON string that would be generated by `JsonObject::printTo()`.
+
+It doesn't include the zero-terminator.
+
+##### Signature
+
+```c++
+size_t measureLength() const
+```
+
+
+
+### JsonObject::measurePrettyLength()
+
+##### Description
+
+Gets the length of string produced by `JsonObject::prettyPrintTo()`.
+
+##### Return value
+
+The number of characters in the JSON string that would be generated by `JsonObject::prettyPrintTo()`.
+
+It doesn't include the zero-terminator.
+
+##### Signature
+
+```c++
+size_t measurePrettyLength() const
+```
+
+
 ### JsonObject::operator[]
 
 ##### Description