diff --git a/app/controllers/process_plates_controller.rb b/app/controllers/process_plates_controller.rb
index 811faa30..70b49c3e 100644
--- a/app/controllers/process_plates_controller.rb
+++ b/app/controllers/process_plates_controller.rb
@@ -25,12 +25,17 @@ def create
     )
     raise format_errors(bed_layout_verification) unless bed_layout_verification.validate_and_create_audits?(params)
 
-    back_to_new_with_message('Success') && return unless receive_plates_process?(params)
+    unless receive_plates_process?(params)
+      back_to_new_with_message('Success')
+      return
+    end
 
     # here on is relevant to 'receiving plates' only
     # the param is called 'source_plates' but we could be working with tube racks or plates etc.
     barcodes = sanitize_barcodes(params[:source_plates])
     raise 'No barcodes were provided' if barcodes.empty?
+    # 20 barcodes takes about 2 mins as of 2020-06-22. This limit is to prevent the request timing out.
+    raise 'Please scan 20 barcodes or fewer' if barcodes.count > 20
 
     responses = call_external_services(barcodes)
     @results = generate_results(barcodes, responses)
diff --git a/app/views/bed_layouts/_default.html.haml b/app/views/bed_layouts/_default.html.haml
index 908eff70..2a58c653 100644
--- a/app/views/bed_layouts/_default.html.haml
+++ b/app/views/bed_layouts/_default.html.haml
@@ -1,6 +1,21 @@
-%label{ :for => "source_plates" } Source plates
+%label{ :for => "source_plates" } Source plates (20 max.)
 = text_area_tag "source_plates", '', :rows => 5,:cols => 17
+.live_results#barcodes_scanned 0 barcodes
 
 :javascript
- $('#source_plates').focus();
- $('#source_plates').trigger('change');
\ No newline at end of file
+  $('#source_plates').focus();
+  $('#source_plates').trigger('change');
+  $('#source_plates').keyup(recalcNumBarcodes);
+
+  function recalcNumBarcodes(){
+    const num_barcodes = find_number_barcodes($('#source_plates').val());
+    const colour = num_barcodes > 20 ? 'red' : 'black';
+
+    $('#barcodes_scanned').text(num_barcodes + ' barcodes').css('color', colour);
+  }
+
+  function find_number_barcodes(text){
+    const barcodes_list_no_blanks = text.split(/\s+/).filter(barcode => Boolean(barcode));
+    const barcodes_list_unique = [...new Set(barcodes_list_no_blanks)];
+    return barcodes_list_unique.length;
+  }
\ No newline at end of file