diff --git a/lib/rackstash/fields/hash.rb b/lib/rackstash/fields/hash.rb
index bdb8d6f..6684104 100644
--- a/lib/rackstash/fields/hash.rb
+++ b/lib/rackstash/fields/hash.rb
@@ -290,6 +290,12 @@ module Rackstash
         @raw.keys
       end
 
+      # @return [Integer] the number of key-value pairs in the hash
+      def length
+        @raw.length
+      end
+      alias size length
+
       # Returns a new {Hash} containing the contents of `hash` and of
       # `self`. If no block is specified, the value for entries with duplicate
       # keys will be that of `hash`. Otherwise the value for each duplicate key
diff --git a/spec/rackstash/fields/hash_spec.rb b/spec/rackstash/fields/hash_spec.rb
index fe01441..deda102 100644
--- a/spec/rackstash/fields/hash_spec.rb
+++ b/spec/rackstash/fields/hash_spec.rb
@@ -495,6 +495,24 @@ describe Rackstash::Fields::Hash do
     end
   end
 
+  describe '#length' do
+    it 'returns the length of the hash' do
+      expect(hash.length).to eql 0
+
+      hash['foo'] = 'bar'
+      expect(hash.length).to eql 1
+
+      hash.clear
+      expect(hash.length).to eql 0
+    end
+
+    it 'can use size as an alias' do
+      expect(hash.size).to eql 0
+      hash['foo'] = 'bar'
+      expect(hash.size).to eql 1
+    end
+  end
+
   describe '#merge!' do
     it 'rejects not hash-convertible arguments' do
       expect { hash.merge!(nil) }.to raise_error TypeError