diff --git a/packages/dd-trace/src/exporters/common/form-data.js b/packages/dd-trace/src/exporters/common/form-data.js
index 91daf3e24be..dacd495b160 100644
--- a/packages/dd-trace/src/exporters/common/form-data.js
+++ b/packages/dd-trace/src/exporters/common/form-data.js
@@ -3,8 +3,6 @@
 const { Readable } = require('stream')
 const id = require('../../id')
 
-const TRAILER_SIZE = 22
-
 class FormData extends Readable {
   constructor () {
     super()
@@ -24,7 +22,7 @@ class FormData extends Readable {
   }
 
   size () {
-    return this._data.reduce((size, chunk) => size + Buffer.byteLength(chunk), TRAILER_SIZE)
+    return this._data.reduce((size, chunk) => size + chunk.length, 0)
   }
 
   getHeaders () {