diff --git a/src/dbwrapper.h b/src/dbwrapper.h
--- a/src/dbwrapper.h
+++ b/src/dbwrapper.h
@@ -56,13 +56,15 @@
     CDataStream ssKey;
     CDataStream ssValue;
 
+    size_t size_estimate;
+
 public:
     /**
      * @param[in] _parent   CDBWrapper that this batch is to be submitted to
      */
     CDBBatch(const CDBWrapper &_parent)
         : parent(_parent), ssKey(SER_DISK, CLIENT_VERSION),
-          ssValue(SER_DISK, CLIENT_VERSION){};
+          ssValue(SER_DISK, CLIENT_VERSION), size_estimate(0){};
 
     template <typename K, typename V> void Write(const K &key, const V &value) {
         ssKey.reserve(DBWRAPPER_PREALLOC_KEY_SIZE);
@@ -75,6 +77,15 @@
         leveldb::Slice slValue(ssValue.data(), ssValue.size());
 
         batch.Put(slKey, slValue);
+        // LevelDB serializes writes as:
+        // - byte: header
+        // - varint: key length (1 byte up to 127B, 2 bytes up to 16383B, ...)
+        // - byte[]: key
+        // - varint: value length
+        // - byte[]: value
+        // The formula below assumes the key and value are both less than 16k.
+        size_estimate += 3 + (slKey.size() > 127) + slKey.size() +
+                         (slValue.size() > 127) + slValue.size();
         ssKey.clear();
         ssValue.clear();
     }
@@ -85,8 +96,16 @@
         leveldb::Slice slKey(ssKey.data(), ssKey.size());
 
         batch.Delete(slKey);
+        // LevelDB serializes erases as:
+        // - byte: header
+        // - varint: key length
+        // - byte[]: key
+        // The formula below assumes the key is less than 16kB.
+        size_estimate += 2 + (slKey.size() > 127) + slKey.size();
         ssKey.clear();
     }
+
+    size_t SizeEstimate() const { return size_estimate; }
 };
 
 class CDBIterator {