diff --git a/lib/utils/pkcs7-padding.js b/lib/utils/pkcs7-padding.js
--- a/lib/utils/pkcs7-padding.js
+++ b/lib/utils/pkcs7-padding.js
@@ -30,6 +30,27 @@
   superblockSizeBlocks: 40,
 };
 
+/**
+ * Calculates length of the data padded with given padding configuration.
+ *
+ * @param {number} inputLength length of the unpadded input (in bytes)
+ * @param paddingConfiguration padding configuration
+ * @returns length of the padded input (in bytes)
+ */
+function calculatePaddedLength(
+  inputLength: number,
+  { blockSizeBytes, superblockSizeBlocks }: PaddingConfiguration = PKCS7_10KB,
+): number {
+  const pkcs7padding = blockSizeBytes - (inputLength % blockSizeBytes);
+  const pkcs7PaddedLen = inputLength + pkcs7padding;
+
+  const numBlocks = pkcs7PaddedLen / blockSizeBytes;
+  const paddingBlocks =
+    superblockSizeBlocks - (numBlocks % superblockSizeBlocks);
+
+  return pkcs7PaddedLen + paddingBlocks * blockSizeBytes;
+}
+
 /**
  * Pads the input using the extended PKCS#7 padding (superblock padding).
  * The input is first padded using the standard PKCS#7 padding, and then
@@ -169,7 +190,7 @@
   return unpaddedData;
 }
 
-export { PKCS7_10KB, pad, unpad };
+export { PKCS7_10KB, pad, unpad, calculatePaddedLength };
 
 // exported for testing purposes only
 export const testing = {
diff --git a/lib/utils/pkcs7-padding.test.js b/lib/utils/pkcs7-padding.test.js
--- a/lib/utils/pkcs7-padding.test.js
+++ b/lib/utils/pkcs7-padding.test.js
@@ -1,7 +1,7 @@
 // @flow
 
 import type { PaddingConfiguration } from './pkcs7-padding';
-import { pad, unpad, testing } from './pkcs7-padding.js';
+import { pad, unpad, testing, calculatePaddedLength } from './pkcs7-padding.js';
 
 const { pkcs7pad, pkcs7unpad, superblockPad, superblockUnpad } = testing;
 
@@ -213,6 +213,27 @@
   });
 });
 
+describe('calculatePaddingLength', () => {
+  it('should calculate the correct padding length', () => {
+    // we're using a 16 byte block size and 4 block superblocks (64 bytes total)
+    // let's say our data is 83 bytes long (1 full superblock + 19 bytes)
+    // we need to pad it to be equal to 2 superblocks (2 * 64 = 128 bytes)
+    // expected padding length is 128-83 = 45 bytes
+    const blockSizeBytes = 16;
+    const superblockSizeBlocks = 4;
+
+    const inputLength = 83;
+    const expectedPaddedLength = 128;
+
+    const calculatedLength = calculatePaddedLength(inputLength, {
+      blockSizeBytes,
+      superblockSizeBlocks,
+    });
+
+    expect(calculatedLength).toBe(expectedPaddedLength);
+  });
+});
+
 function generateRandomData(length: number): Uint8Array {
   const data = new Uint8Array(length);
   for (let i = 0; i < length; i++) {