diff --git a/INSTALL.md b/INSTALL.md
index 33023af6..02b496eb 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -43,7 +43,6 @@ There are a couple of environment variables you can set to configure OSEM. Check
 | OSEM_FACEBOOK_SECRET | *string*		| OMNIAUTH Developer Secret for Facebook
 | OSEM_GITHUB_KEY | *string*			| OMNIAUTH Developer Key for GitHub
 | OSEM_GITHUB_SECRET | *string*			| OMNIAUTH Developer Secret for GitHub
-| OSEM_SCHEDULE_CELL_SIZE | *integer*		| Schedule timeslot size to use (in minutes), should be greater than zero, should be divisor of 60
 | OSEM_SMTP_ADDRESS		| smtp.opensuse.org		| The smtp server to use
 | OSEM_SMTP_PORT		| *int*				| The port on the smtp server
 | OSEM_SMTP_USERNAME		| *string*			| The user for the smtp server
diff --git a/app.json b/app.json
index 6b28f6b9..f77f6c9c 100644
--- a/app.json
+++ b/app.json
@@ -54,10 +54,6 @@
       "description": "The user for the smtp server",
       "required": false
     },
-    "OSEM_SCHEDULE_CELL_SIZE": {
-      "description": "Schedule timeslot size in minutes",
-      "required": false
-    },
     "RACK_ENV": {
       "required": false
     },
diff --git a/app/controllers/admin/programs_controller.rb b/app/controllers/admin/programs_controller.rb
index 77b45a57..772ae779 100644
--- a/app/controllers/admin/programs_controller.rb
+++ b/app/controllers/admin/programs_controller.rb
@@ -12,13 +12,15 @@ module Admin
       @program = @conference.program
       @program.assign_attributes(program_params)
       send_mail_on_schedule_public = @program.notify_on_schedule_public?
+      event_schedules_count_was = @program.event_schedules.count
 
       if @program.update_attributes(program_params)
         ConferenceScheduleUpdateMailJob.perform_later(@conference) if send_mail_on_schedule_public
         respond_to do |format|
           format.html do
-            redirect_to admin_conference_program_path(@conference.short_title),
-                        notice: 'The program was successfully updated.'
+            notice = 'The program was successfully updated.'
+            notice += ' You changed schedule interval and some events were unscheduled.' if @program.event_schedules.count != event_schedules_count_was
+            redirect_to admin_conference_program_path(@conference.short_title), notice: notice
           end
           format.js { render json: {} }
         end
@@ -36,7 +38,7 @@ module Admin
     private
 
     def program_params
-      params.require(:program).permit(:rating, :schedule_public, :schedule_fluid, :languages, :blind_voting, :voting_start_date, :voting_end_date, :selected_schedule_id)
+      params.require(:program).permit(:rating, :schedule_public, :schedule_interval, :schedule_fluid, :languages, :blind_voting, :voting_start_date, :voting_end_date, :selected_schedule_id)
     end
   end
 end
diff --git a/app/controllers/schedules_controller.rb b/app/controllers/schedules_controller.rb
index 0b135328..c759d337 100644
--- a/app/controllers/schedules_controller.rb
+++ b/app/controllers/schedules_controller.rb
@@ -13,7 +13,7 @@ class SchedulesController < ApplicationController
 
     @events_xml = schedules.map(&:event).group_by{ |event| event.time.to_date } if schedules
     @dates = @conference.start_date..@conference.end_date
-    @step_minutes = EventType::LENGTH_STEP.minutes
+    @step_minutes = @program.schedule_interval.minutes
     @conf_start = @conference.start_hour
     @conf_period = @conference.end_hour - @conf_start
 
diff --git a/app/models/event_type.rb b/app/models/event_type.rb
index 50d8d551..47da514f 100644
--- a/app/models/event_type.rb
+++ b/app/models/event_type.rb
@@ -15,17 +15,13 @@ class EventType < ActiveRecord::Base
 
   alias_attribute :name, :title
 
-  # If LENGTH_STEP must be divisor of 60, otherwise the schedule wont be displayed properly
-
-  LENGTH_STEP = defined?(SCHEDULE_CELL_SIZE) ? SCHEDULE_CELL_SIZE : 15
-
   private
 
   ##
-  # Check if length is multiple of LENGTH_STEP. Used as validation.
+  # Check if length is a divisor of program schedule cell size. Used as validation.
   #
   def length_step
-    errors.add(:length, "must be multiple of #{LENGTH_STEP}") if length % LENGTH_STEP != 0
+    errors.add(:length, "must be a divisor of #{program.schedule_interval}") if program && length % program.schedule_interval != 0
   end
 
   def capitalize_color
diff --git a/app/models/program.rb b/app/models/program.rb
index f8b46b18..ff0ab094 100644
--- a/app/models/program.rb
+++ b/app/models/program.rb
@@ -38,6 +38,7 @@ class Program < ActiveRecord::Base
       where(state: :confirmed, is_highlight: true)
     end
   end
+  has_many :event_schedules, through: :events
 
   has_many :event_users, through: :events
   has_many :speakers, -> { distinct }, through: :event_users, source: :user do
@@ -52,11 +53,15 @@ class Program < ActiveRecord::Base
 
 #   validates :conference_id, presence: true, uniqueness: true
   validates :rating, numericality: { greater_than_or_equal_to: 0, less_than_or_equal_to: 10, only_integer: true }
+  validates :schedule_interval, numericality: { greater_than_or_equal_to: 5, less_than_or_equal_to: 60 }, presence: true
+  validate :schedule_interval_divisor_60
   validate :voting_start_date_before_end_date
   validate :voting_dates_exist
 
   after_create :create_event_types
   after_create :create_difficulty_levels
+  after_save :unschedule_unfit_events, if: :schedule_interval_changed?
+  after_save :normalize_event_types_length, if: :schedule_interval_changed?
   validate :check_languages_format
 
   # Returns all event_schedules for the selected schedule ordered by start_time
@@ -199,4 +204,31 @@ class Program < ActiveRecord::Base
     # We check if every language is a valid ISO 639-1 language
     errors.add(:languages, 'must be ISO 639-1 valid codes') unless languages_array.select{ |x| ISO_639.find(x).nil? }.empty?
   end
+
+  ##
+  # Check if schedule_interval is a divisor of 60 minutes
+  #
+  def schedule_interval_divisor_60
+    errors.add(:schedule_interval, 'must be a divisor of 60') if schedule_interval > 0 && 60 % schedule_interval > 0
+  end
+
+  ##
+  # Unschedule all the events which don't fit
+  #
+  def unschedule_unfit_events
+    unfit_schedules = event_schedules.select do |event_schedule|
+      event_schedule.start_time.min % schedule_interval > 0
+    end
+    EventSchedule.where(id: unfit_schedules.map(&:id)).destroy_all
+  end
+
+  ##
+  # Change event type length according schedule interval
+  #
+  def normalize_event_types_length
+    event_types.each do |event_type|
+      new_length = event_type.length > schedule_interval ? event_type.length - (event_type.length % schedule_interval) : schedule_interval
+      event_type.update_attributes length: new_length
+    end
+  end
 end
diff --git a/app/serializers/event_serializer.rb b/app/serializers/event_serializer.rb
index c2dffbeb..d58d23d2 100644
--- a/app/serializers/event_serializer.rb
+++ b/app/serializers/event_serializer.rb
@@ -26,6 +26,6 @@ class EventSerializer < ActiveModel::Serializer
   end
 
   def length
-    object.event_type.try(:length) || EventType::LENGTH_STEP
+    object.event_type.try(:length) || object.event_type.program.schedule_interval
   end
 end
diff --git a/app/views/admin/event_types/_form.html.haml b/app/views/admin/event_types/_form.html.haml
index 3f3702b4..51a0ad99 100644
--- a/app/views/admin/event_types/_form.html.haml
+++ b/app/views/admin/event_types/_form.html.haml
@@ -10,7 +10,7 @@
   .col-md-12
     = semantic_form_for(@event_type, url: (@event_type.new_record? ? admin_conference_program_event_types_path : admin_conference_program_event_type_path(@conference.short_title, @event_type))) do |f|
       = f.input :title
-      = f.input :length, input_html: {size: 3, type: 'number', step: EventType::LENGTH_STEP, min: EventType::LENGTH_STEP}
+      = f.input :length, input_html: {size: 3, type: 'number', step: @event_type.program.schedule_interval, min: @event_type.program.schedule_interval}
       = f.input :description
       = f.input :minimum_abstract_length, input_html: {size: 3}
       = f.input :maximum_abstract_length, input_html: {size: 3}
diff --git a/app/views/admin/programs/_form.html.haml b/app/views/admin/programs/_form.html.haml
index 8eb5ea47..035093f0 100644
--- a/app/views/admin/programs/_form.html.haml
+++ b/app/views/admin/programs/_form.html.haml
@@ -9,6 +9,7 @@
       = f.input :schedule_fluid, label: 'Allow submitters to change their event after it is scheduled'
       = f.input :rating, hint: 'Enter the number of different rating levels you want to have for voting on proposals. Enter 0 if you do not want to vote on proposals.'
       = f.input :languages, hint: "Enter the languages allowed for events as values of #{link_to('ISO 639-1', 'http://www.loc.gov/standards/iso639-2/php/code_list.php', target: "_blank")} language codes separated with commas. The first language would be the default language. Leave it blank if you do not want to specify languages.".html_safe
+      = f.input :schedule_interval, hint: "It is the minimal time interval of your schedule. The value should be 5, 6, 10, 12, 15, 20, 30 or 60. Warning! Some events could be unscheduled when changing this value."
       = f.input :blind_voting, hint: 'Enable this feature if you do not want to show voting results and voters prior to user submitting a vote. For the feature to work you need to set the voting dates below as well'
       = f.input :voting_start_date, as: :string, input_html: { id: 'datetimepicker-voting_start_date', readonly: true, value: (f.object.voting_start_date.to_formatted_s(:db_without_seconds) unless f.object.voting_start_date.nil?) }
       = f.input :voting_end_date, as: :string, input_html: { id: 'datetimepicker-voting_start_date', readonly: true, value: (f.object.voting_end_date.to_formatted_s(:db_without_seconds) unless f.object.voting_end_date.nil?) }
diff --git a/app/views/admin/programs/show.html.haml b/app/views/admin/programs/show.html.haml
index 085a47c1..47e50fb6 100644
--- a/app/views/admin/programs/show.html.haml
+++ b/app/views/admin/programs/show.html.haml
@@ -49,6 +49,11 @@
             Yes
           - else
             No
+        %dt
+          Schedule interval
+        %dd
+          = @program.schedule_interval
+          minutes
 
         %h3 Voting Options
         %hr
diff --git a/app/views/admin/schedules/_day_tab.html.haml b/app/views/admin/schedules/_day_tab.html.haml
index 61f6e862..7bfe3ec6 100644
--- a/app/views/admin/schedules/_day_tab.html.haml
+++ b/app/views/admin/schedules/_day_tab.html.haml
@@ -1,5 +1,5 @@
-- compact_grid = EventType::LENGTH_STEP < 15
-- cells_per_hour = 60 / EventType::LENGTH_STEP
+- compact_grid = @program.schedule_interval < 15
+- cells_per_hour = 60 / @program.schedule_interval
 / use smaller cell heights for more compact grids
 - cell_height = compact_grid ? 32 : 58
 - date_event_schedules = @event_schedules.select{ |e| e.start_time.to_date.eql? date }
@@ -11,7 +11,7 @@
         = room.name
       - (@conference.start_hour * cells_per_hour..@conference.end_hour * cells_per_hour).each do |slot|
         - hour = slot / cells_per_hour
-        - minutes = (EventType::LENGTH_STEP * (slot % cells_per_hour)).to_s.rjust(2, '0')
+        - minutes = (@program.schedule_interval * (slot % cells_per_hour)).to_s.rjust(2, '0')
         - time = "#{hour}:#{minutes}"
         .schedule-room-slot{ id: "schedule-room-#{room.guid}-#{hour}-#{minutes}", |
                              room_id: room.id, |
diff --git a/app/views/admin/schedules/_event.html.haml b/app/views/admin/schedules/_event.html.haml
index 3c9c0c75..3a13323b 100644
--- a/app/views/admin/schedules/_event.html.haml
+++ b/app/views/admin/schedules/_event.html.haml
@@ -1,6 +1,6 @@
-- cells_length = event.event_type.length / EventType::LENGTH_STEP
+- cells_length = event.event_type.length / @program.schedule_interval
 / this height fits the room cells
-- compact_grid = EventType::LENGTH_STEP < 15
+- compact_grid = @program.schedule_interval < 15
 - single_cell_height =  compact_grid ? 32 : 58
 - height = (cells_length * single_cell_height)
 - height -= 23 unless compact_grid
diff --git a/app/views/schedules/_carousel.html.haml b/app/views/schedules/_carousel.html.haml
index 5c5acc29..ce28e909 100644
--- a/app/views/schedules/_carousel.html.haml
+++ b/app/views/schedules/_carousel.html.haml
@@ -1,4 +1,4 @@
-- intervals = hrs_per_slide * 60 / EventType::LENGTH_STEP + 1
+- intervals = hrs_per_slide * 60 / @conference.program.schedule_interval + 1
 - width = 85 / intervals
 - carousel_number = (@conf_period / hrs_per_slide.to_f).ceil
 .carousel.slide{ id: "carousel-#{ date }-#{ hrs_per_slide }", |
@@ -41,7 +41,7 @@
 
                     - if event_schedule
                       / There is an event, calculate the span and show it
-                      - event_span =  (event_schedule.end_time.to_i - start_room_time.to_i) / 60 / EventType::LENGTH_STEP
+                      - event_span =  (event_schedule.end_time.to_i - start_room_time.to_i) / 60 / @conference.program.schedule_interval
                       - span = ((event_span + i - 1 ) > intervals ? intervals  + 1 - i : event_span)
                       = render partial: 'schedule_item', locals: {event: event_schedule.event, event_schedule: event_schedule, span: span, width: width}
                     - else
diff --git a/app/views/schedules/show.xml.haml b/app/views/schedules/show.xml.haml
index 953a331f..d84e98de 100644
--- a/app/views/schedules/show.xml.haml
+++ b/app/views/schedules/show.xml.haml
@@ -6,7 +6,7 @@
     %start= @conference.start_date
     %end= @conference.end_date
     %days= (@conference.end_date - @conference.start_date).to_i + 1
-    %timeslot_duration= length_timestamp(EventType::LENGTH_STEP)
+    %timeslot_duration= length_timestamp(@conference.program.schedule_interval)
 
   - if @events_xml.any?
     - @events_xml.keys.each.with_index(1) do |day, index|
diff --git a/config/initializers/schedule_parameters.rb b/config/initializers/schedule_parameters.rb
deleted file mode 100644
index 7d1ca08d..00000000
--- a/config/initializers/schedule_parameters.rb
+++ /dev/null
@@ -1,6 +0,0 @@
-#sanitize the OSEM_SCHEUDLE_CELL_SIZE to be used for EventType::LENGTH_STEP
-sched_cell_size = ENV['OSEM_SCHEDULE_CELL_SIZE'].to_i
-
-if (sched_cell_size > 0 and 60 % sched_cell_size == 0)
-  SCHEDULE_CELL_SIZE = sched_cell_size
-end
diff --git a/db/migrate/20170302145716_add_schedule_interval_to_programs.rb b/db/migrate/20170302145716_add_schedule_interval_to_programs.rb
new file mode 100644
index 00000000..617aaf1e
--- /dev/null
+++ b/db/migrate/20170302145716_add_schedule_interval_to_programs.rb
@@ -0,0 +1,5 @@
+class AddScheduleIntervalToPrograms < ActiveRecord::Migration
+  def change
+    add_column :programs, :schedule_interval, :integer, default: 15, null: false
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 34c30a04..ab95b4dc 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170213145807) do
+ActiveRecord::Schema.define(version: 20170302145716) do
 
   create_table "ahoy_events", force: :cascade do |t|
     t.uuid     "visit_id",   limit: 16
@@ -289,6 +289,7 @@ ActiveRecord::Schema.define(version: 20170213145807) do
     t.datetime "voting_start_date"
     t.datetime "voting_end_date"
     t.integer  "selected_schedule_id"
+    t.integer  "schedule_interval",    default: 15,    null: false
   end
 
   add_index "programs", ["selected_schedule_id"], name: "index_programs_on_selected_schedule_id"
diff --git a/dotenv.example b/dotenv.example
index b9c2a668..ec2715ea 100644
--- a/dotenv.example
+++ b/dotenv.example
@@ -57,6 +57,3 @@ OSEM_SMTP_DOMAIN=""
 
 # Enable the usage of the devise ichain plugin
 OSEM_ICHAIN_ENABLED=false
-
-# Schedule grid parameters, cell size in minutes
-OSEM_SCHEDULE_CELL_SIZE=15
diff --git a/spec/models/program_spec.rb b/spec/models/program_spec.rb
index f491499b..ac720def 100644
--- a/spec/models/program_spec.rb
+++ b/spec/models/program_spec.rb
@@ -13,6 +13,7 @@ describe Program do
     it { is_expected.to have_many(:tracks).dependent(:destroy) }
     it { is_expected.to have_many(:difficulty_levels).dependent(:destroy) }
     it { is_expected.to have_many(:events).dependent(:destroy) }
+    it { is_expected.to have_many(:event_schedules).through(:events) }
     it { is_expected.to have_many(:event_users).through(:events) }
     it { is_expected.to have_many(:speakers).through(:event_users).source(:user) }
 
@@ -32,6 +33,18 @@ describe Program do
 
     it { is_expected.to validate_numericality_of(:rating).is_greater_than_or_equal_to(0).is_less_than_or_equal_to(10).only_integer }
 
+    it { is_expected.to validate_numericality_of(:schedule_interval).is_greater_than_or_equal_to(5).is_less_than_or_equal_to(60) }
+
+    describe 'schedule_interval_divisor_60' do
+      it 'is valid, when schedule_interval is divisor of 60' do
+        expect(build(:program, schedule_interval: 20)).to be_valid
+      end
+
+      it 'is not valid, when schedule_interval is not divisor of 60' do
+        expect(build(:program, schedule_interval: 35)).to_not be_valid
+      end
+    end
+
     describe 'voting_start_date_before_end_date' do
       it 'is valid, when voting_start_date is the same day as voting_end_date' do
         expect(build(:program, voting_start_date: Date.today, voting_end_date: Date.today)).to be_valid
@@ -167,6 +180,34 @@ describe Program do
     end
   end
 
+  describe 'excecutes after_save functions' do
+    it 'and unschedule unfit events if schedule interval was changed' do
+      start_date = program.conference.start_date.to_datetime.change(hour: program.conference.start_hour)
+      create(:event_schedule, event: create(:event, program: program), start_time: start_date.change(min: program.schedule_interval))
+      create(:event_schedule, event: create(:event, program: program), start_time: start_date)
+      expect(program.event_schedules.count).to eq 2
+
+      program.schedule_interval = 10
+      program.save!
+      program.reload
+      expect(program.event_schedules.count).to eq 1
+      expect(program.event_schedules.first.start_time).to eq start_date
+    end
+
+    it 'and change event type length if schedule interval was changed' do
+      program.schedule_interval = 5
+      program.save!
+
+      program.event_types.first.update_attributes length: 5
+      program.event_types.last.update_attributes length: 25
+      create(:event_type, program: program, length: 30)
+
+      program.schedule_interval = 10
+      program.save!
+      expect(program.event_types.pluck(:length).sort).to eq [10, 20, 30]
+    end
+  end
+
   describe 'languages' do
     it "is not valid if languages aren't two letters separated by commas" do
       program.languages = 'eng, De es'