diff --git a/cpp/src/parquet/encoding_test.cc b/cpp/src/parquet/encoding_test.cc
index 60f334b2cfc58..ea0029f4c7d7f 100644
--- a/cpp/src/parquet/encoding_test.cc
+++ b/cpp/src/parquet/encoding_test.cc
@@ -1238,8 +1238,7 @@ class TestByteStreamSplitEncoding : public TestEncodingBase<Type> {
 
     encoder->PutSpaced(draws_, num_values_, valid_bits, valid_bits_offset);
     encode_buffer_ = encoder->FlushValues();
-    ASSERT_EQ(encode_buffer_->size(),
-              static_cast<int>(sizeof(c_type)) * (num_values_ - null_count));
+    ASSERT_EQ(encode_buffer_->size(), physical_byte_width() * (num_values_ - null_count));
     decoder->SetData(num_values_ - null_count, encode_buffer_->data(),
                      static_cast<int>(encode_buffer_->size()));
     auto values_decoded = decoder->DecodeSpaced(decode_buf_, num_values_, null_count,
@@ -1302,6 +1301,11 @@ class TestByteStreamSplitEncoding : public TestEncodingBase<Type> {
       ASSERT_EQ(expected_encoded_data[i], encoded_data_raw[i]);
     }
   }
+
+  int physical_byte_width() const {
+    return std::is_same_v<c_type, FLBA> ? descr_->type_length()
+                                        : static_cast<int>(sizeof(c_type));
+  }
 };
 
 template <typename c_type>