diff --git a/esphome/components/hmac_md5/hmac_md5.h b/esphome/components/hmac_md5/hmac_md5.h
index b83b9d5421b..fb9479e3afa 100644
--- a/esphome/components/hmac_md5/hmac_md5.h
+++ b/esphome/components/hmac_md5/hmac_md5.h
@@ -30,7 +30,7 @@ class HmacMD5 {
   void get_bytes(uint8_t *output);
 
   /// Retrieve the HMAC-MD5 digest as hex characters.
-  /// The output must be able to hold 32 bytes or more.
+  /// The output must be able to hold 33 bytes or more (32 hex chars + null terminator).
   void get_hex(char *output);
 
   /// Compare the digest against a provided byte-encoded digest (16 bytes).
diff --git a/esphome/components/hmac_sha256/hmac_sha256.h b/esphome/components/hmac_sha256/hmac_sha256.h
index fa6b64aa949..85622cac46b 100644
--- a/esphome/components/hmac_sha256/hmac_sha256.h
+++ b/esphome/components/hmac_sha256/hmac_sha256.h
@@ -35,7 +35,7 @@ class HmacSHA256 {
   void get_bytes(uint8_t *output);
 
   /// Retrieve the HMAC-SHA256 digest as hex characters.
-  /// The output must be able to hold 64 bytes or more.
+  /// The output must be able to hold 65 bytes or more (64 hex chars + null terminator).
   void get_hex(char *output);
 
   /// Compare the digest against a provided byte-encoded digest (32 bytes).
diff --git a/esphome/core/hash_base.h b/esphome/core/hash_base.h
index cc4fcdf9202..0c1c2dce330 100644
--- a/esphome/core/hash_base.h
+++ b/esphome/core/hash_base.h
@@ -25,7 +25,7 @@ class HashBase {
   /// Retrieve the hash as bytes
   void get_bytes(uint8_t *output) { memcpy(output, this->digest_, this->get_size()); }
 
-  /// Retrieve the hash as hex characters
+  /// Retrieve the hash as hex characters. Output buffer must hold get_size() * 2 + 1 bytes.
   void get_hex(char *output) { format_hex_to(output, this->get_size() * 2 + 1, this->digest_, this->get_size()); }
 
   /// Compare the hash against a provided byte-encoded hash