diff --git a/python/ray/actor.py b/python/ray/actor.py
index 690f8ce1c..3886e1927 100644
--- a/python/ray/actor.py
+++ b/python/ray/actor.py
@@ -48,7 +48,7 @@ def compute_actor_handle_id(actor_handle_id, num_forks):
     handle_id_hash.update(actor_handle_id.id())
     handle_id_hash.update(str(num_forks).encode("ascii"))
     handle_id = handle_id_hash.digest()
-    assert len(handle_id) == 20
+    assert len(handle_id) == ray_constants.ID_SIZE
     return ray.ObjectID(handle_id)
 
 
@@ -80,7 +80,7 @@ def compute_actor_handle_id_non_forked(actor_id, actor_handle_id,
     handle_id_hash.update(actor_handle_id.id())
     handle_id_hash.update(current_task_id.id())
     handle_id = handle_id_hash.digest()
-    assert len(handle_id) == 20
+    assert len(handle_id) == ray_constants.ID_SIZE
     return ray.ObjectID(handle_id)
 
 
@@ -110,7 +110,7 @@ def compute_actor_method_function_id(class_name, attr):
     function_id_hash.update(class_name.encode("ascii"))
     function_id_hash.update(attr.encode("ascii"))
     function_id = function_id_hash.digest()
-    assert len(function_id) == 20
+    assert len(function_id) == ray_constants.ID_SIZE
     return ray.ObjectID(function_id)
 
 
diff --git a/python/ray/common/test/test.py b/python/ray/common/test/test.py
index 4ae867ff9..cd36b697b 100644
--- a/python/ray/common/test/test.py
+++ b/python/ray/common/test/test.py
@@ -8,24 +8,23 @@ import sys
 import unittest
 
 import ray.local_scheduler as local_scheduler
-
-ID_SIZE = 20
+import ray.ray_constants as ray_constants
 
 
 def random_object_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_function_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_driver_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_task_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 BASE_SIMPLE_OBJECTS = [
@@ -110,15 +109,17 @@ class TestObjectID(unittest.TestCase):
         self.assertRaises(Exception, lambda: pickle.dumps(h))
 
     def test_equality_comparisons(self):
-        x1 = local_scheduler.ObjectID(ID_SIZE * b"a")
-        x2 = local_scheduler.ObjectID(ID_SIZE * b"a")
-        y1 = local_scheduler.ObjectID(ID_SIZE * b"b")
-        y2 = local_scheduler.ObjectID(ID_SIZE * b"b")
+        x1 = local_scheduler.ObjectID(ray_constants.ID_SIZE * b"a")
+        x2 = local_scheduler.ObjectID(ray_constants.ID_SIZE * b"a")
+        y1 = local_scheduler.ObjectID(ray_constants.ID_SIZE * b"b")
+        y2 = local_scheduler.ObjectID(ray_constants.ID_SIZE * b"b")
         self.assertEqual(x1, x2)
         self.assertEqual(y1, y2)
         self.assertNotEqual(x1, y1)
 
-        random_strings = [np.random.bytes(ID_SIZE) for _ in range(256)]
+        random_strings = [
+            np.random.bytes(ray_constants.ID_SIZE) for _ in range(256)
+        ]
         object_ids1 = [
             local_scheduler.ObjectID(random_strings[i]) for i in range(256)
         ]
diff --git a/python/ray/experimental/state.py b/python/ray/experimental/state.py
index fda6314cb..299fa981a 100644
--- a/python/ray/experimental/state.py
+++ b/python/ray/experimental/state.py
@@ -13,6 +13,7 @@ import time
 
 import ray
 import ray.gcs_utils
+import ray.ray_constants as ray_constants
 from ray.utils import (decode, binary_to_object_id, binary_to_hex,
                        hex_to_binary)
 
@@ -496,7 +497,7 @@ class GlobalState(object):
 
         else:
             # This is the raylet code path.
-            NIL_CLIENT_ID = 20 * b"\xff"
+            NIL_CLIENT_ID = ray_constants.ID_SIZE * b"\xff"
             message = self.redis_client.execute_command(
                 "RAY.TABLE_LOOKUP", ray.gcs_utils.TablePrefix.CLIENT, "",
                 NIL_CLIENT_ID)
@@ -1235,7 +1236,7 @@ class GlobalState(object):
         for key in actor_keys:
             info = self.redis_client.hgetall(key)
             actor_id = key[len("Actor:"):]
-            assert len(actor_id) == 20
+            assert len(actor_id) == ray_constants.ID_SIZE
             actor_info[binary_to_hex(actor_id)] = {
                 "class_id": binary_to_hex(info[b"class_id"]),
                 "driver_id": binary_to_hex(info[b"driver_id"]),
diff --git a/python/ray/global_scheduler/test/test.py b/python/ray/global_scheduler/test/test.py
index 0e4af0684..d8ef98264 100644
--- a/python/ray/global_scheduler/test/test.py
+++ b/python/ray/global_scheduler/test/test.py
@@ -18,32 +18,32 @@ import ray.plasma as plasma
 from ray.plasma.utils import create_object
 from ray import services
 from ray.experimental import state
+import ray.ray_constants as ray_constants
 import pyarrow as pa
 
 USE_VALGRIND = False
 PLASMA_STORE_MEMORY = 1000000000
-ID_SIZE = 20
 NUM_CLUSTER_NODES = 2
 
-NIL_WORKER_ID = 20 * b"\xff"
-NIL_OBJECT_ID = 20 * b"\xff"
-NIL_ACTOR_ID = 20 * b"\xff"
+NIL_WORKER_ID = ray_constants.ID_SIZE * b"\xff"
+NIL_OBJECT_ID = ray_constants.ID_SIZE * b"\xff"
+NIL_ACTOR_ID = ray_constants.ID_SIZE * b"\xff"
 
 
 def random_driver_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_task_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_function_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_object_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def new_port():
diff --git a/python/ray/local_scheduler/test/test.py b/python/ray/local_scheduler/test/test.py
index 6b7025841..b35d609de 100644
--- a/python/ray/local_scheduler/test/test.py
+++ b/python/ray/local_scheduler/test/test.py
@@ -12,28 +12,28 @@ import unittest
 
 import ray.local_scheduler as local_scheduler
 import ray.plasma as plasma
+import ray.ray_constants as ray_constants
 import pyarrow as pa
 
 USE_VALGRIND = False
-ID_SIZE = 20
 
-NIL_WORKER_ID = 20 * b"\xff"
+NIL_WORKER_ID = ray_constants.ID_SIZE * b"\xff"
 
 
 def random_object_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_driver_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_task_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def random_function_id():
-    return local_scheduler.ObjectID(np.random.bytes(ID_SIZE))
+    return local_scheduler.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 class TestLocalSchedulerClient(unittest.TestCase):
diff --git a/python/ray/monitor.py b/python/ray/monitor.py
index 0d423ea82..d659afd81 100644
--- a/python/ray/monitor.py
+++ b/python/ray/monitor.py
@@ -16,14 +16,14 @@ from ray.autoscaler.autoscaler import LoadMetrics, StandardAutoscaler
 import ray.cloudpickle as pickle
 import ray.gcs_utils
 import ray.utils
+import ray.ray_constants as ray_constants
 from ray.services import get_ip_address, get_port
 from ray.utils import binary_to_hex, binary_to_object_id, hex_to_binary
 from ray.worker import NIL_ACTOR_ID
 
 # These variables must be kept in sync with the C codebase.
 # common/common.h
-DB_CLIENT_ID_SIZE = 20
-NIL_ID = b"\xff" * DB_CLIENT_ID_SIZE
+NIL_ID = b"\xff" * ray_constants.ID_SIZE
 
 # common/task.h
 TASK_STATUS_LOST = 32
@@ -348,8 +348,8 @@ class Monitor(object):
         This resets the number of heartbeats that we've missed from this plasma
         manager.
         """
-        # The first DB_CLIENT_ID_SIZE characters are the client ID.
-        db_client_id = data[:DB_CLIENT_ID_SIZE]
+        # The first ray_constants.ID_SIZE characters are the client ID.
+        db_client_id = data[:ray_constants.ID_SIZE]
         # Reset the number of heartbeats that we've missed from this plasma
         # manager.
         self.live_plasma_managers[db_client_id] = 0
diff --git a/python/ray/plasma/test/test.py b/python/ray/plasma/test/test.py
index 0ec424d6a..e5a2d27ea 100644
--- a/python/ray/plasma/test/test.py
+++ b/python/ray/plasma/test/test.py
@@ -18,6 +18,7 @@ import unittest
 import ray
 from ray.plasma.utils import (random_object_id, create_object_with_id,
                               create_object)
+import ray.ray_constants as ray_constants
 from ray import services
 import pyarrow as pa
 import pyarrow.plasma as plasma
@@ -377,7 +378,7 @@ class TestPlasmaManager(unittest.TestCase):
         # Make sure that wait returns when the requested number of object IDs
         # are available and does not wait for all object IDs to be available.
         object_ids = [random_object_id() for _ in range(9)] + \
-                     [plasma.ObjectID(20 * b'\x00')]
+                     [plasma.ObjectID(ray_constants.ID_SIZE * b'\x00')]
         object_ids_perm = object_ids[:]
         random.shuffle(object_ids_perm)
         for i in range(10):
diff --git a/python/ray/plasma/utils.py b/python/ray/plasma/utils.py
index 956502e75..45feb0b1d 100644
--- a/python/ray/plasma/utils.py
+++ b/python/ray/plasma/utils.py
@@ -6,10 +6,11 @@ import numpy as np
 import random
 
 import pyarrow.plasma as plasma
+import ray.ray_constants as ray_constants
 
 
 def random_object_id():
-    return plasma.ObjectID(np.random.bytes(20))
+    return plasma.ObjectID(np.random.bytes(ray_constants.ID_SIZE))
 
 
 def generate_metadata(length):
diff --git a/python/ray/remote_function.py b/python/ray/remote_function.py
index a3d8c450e..fb963393d 100644
--- a/python/ray/remote_function.py
+++ b/python/ray/remote_function.py
@@ -6,6 +6,7 @@ import copy
 import hashlib
 import inspect
 
+import ray.ray_constants as ray_constants
 import ray.signature
 
 # Default parameters for remote functions.
@@ -37,7 +38,7 @@ def compute_function_id(function):
         pass
     # Compute the function ID.
     function_id = function_id_hash.digest()
-    assert len(function_id) == 20
+    assert len(function_id) == ray_constants.ID_SIZE
     function_id = ray.ObjectID(function_id)
 
     return function_id
diff --git a/python/ray/utils.py b/python/ray/utils.py
index 208a704a9..d5c348289 100644
--- a/python/ray/utils.py
+++ b/python/ray/utils.py
@@ -17,14 +17,13 @@ import ray.local_scheduler
 import ray.ray_constants as ray_constants
 
 ERROR_KEY_PREFIX = b"Error:"
-DRIVER_ID_LENGTH = 20
 
 
 def _random_string():
     id_hash = hashlib.sha1()
     id_hash.update(uuid.uuid4().bytes)
     id_bytes = id_hash.digest()
-    assert len(id_bytes) == 20
+    assert len(id_bytes) == ray_constants.ID_SIZE
     return id_bytes
 
 
@@ -157,14 +156,14 @@ def random_string():
     deterministic manner, then we will need to make some changes here.
 
     Returns:
-        A random byte string of length 20.
+        A random byte string of length ray_constants.ID_SIZE.
     """
     # Get the state of the numpy random number generator.
     numpy_state = np.random.get_state()
     # Try to use true randomness.
     np.random.seed(None)
     # Generate the random ID.
-    random_id = np.random.bytes(20)
+    random_id = np.random.bytes(ray_constants.ID_SIZE)
     # Reset the state of the numpy random number generator.
     np.random.set_state(numpy_state)
     return random_id
diff --git a/python/ray/worker.py b/python/ray/worker.py
index d00c28dda..1c3714284 100644
--- a/python/ray/worker.py
+++ b/python/ray/worker.py
@@ -47,16 +47,14 @@ SILENT_MODE = 3
 PYTHON_MODE = 4
 
 ERROR_KEY_PREFIX = b"Error:"
-DRIVER_ID_LENGTH = 20
-ERROR_ID_LENGTH = 20
 
 # This must match the definition of NIL_ACTOR_ID in task.h.
-NIL_ID = 20 * b"\xff"
+NIL_ID = ray_constants.ID_SIZE * b"\xff"
 NIL_LOCAL_SCHEDULER_ID = NIL_ID
 NIL_FUNCTION_ID = NIL_ID
 NIL_ACTOR_ID = NIL_ID
 NIL_ACTOR_HANDLE_ID = NIL_ID
-NIL_CLIENT_ID = 20 * b"\xff"
+NIL_CLIENT_ID = ray_constants.ID_SIZE * b"\xff"
 
 # This must be kept in sync with the `error_types` array in
 # common/state/error_table.h.
@@ -1207,13 +1205,13 @@ def error_applies_to_driver(error_key, worker=global_worker):
     """Return True if the error is for this driver and false otherwise."""
     # TODO(rkn): Should probably check that this is only called on a driver.
     # Check that the error key is formatted as in push_error_to_driver.
-    assert len(error_key) == (len(ERROR_KEY_PREFIX) + DRIVER_ID_LENGTH + 1 +
-                              ERROR_ID_LENGTH), error_key
+    assert len(error_key) == (len(ERROR_KEY_PREFIX) + ray_constants.ID_SIZE + 1
+                              + ray_constants.ID_SIZE), error_key
     # If the driver ID in the error message is a sequence of all zeros, then
     # the message is intended for all drivers.
-    generic_driver_id = DRIVER_ID_LENGTH * b"\x00"
+    generic_driver_id = ray_constants.ID_SIZE * b"\x00"
     driver_id = error_key[len(ERROR_KEY_PREFIX):(
-        len(ERROR_KEY_PREFIX) + DRIVER_ID_LENGTH)]
+        len(ERROR_KEY_PREFIX) + ray_constants.ID_SIZE)]
     return (driver_id == worker.task_driver_id.id()
             or driver_id == generic_driver_id)
 
@@ -1951,7 +1949,7 @@ def print_error_messages_raylet(worker):
             assert gcs_entry.EntriesLength() == 1
             error_data = ray.gcs_utils.ErrorTableData.GetRootAsErrorTableData(
                 gcs_entry.Entries(0), 0)
-            NIL_JOB_ID = 20 * b"\x00"
+            NIL_JOB_ID = ray_constants.ID_SIZE * b"\x00"
             job_id = error_data.JobId()
             if job_id not in [worker.task_driver_id.id(), NIL_JOB_ID]:
                 continue
@@ -2182,7 +2180,8 @@ def connect(info,
         else:
             # Try to use true randomness.
             np.random.seed(None)
-        worker.current_task_id = ray.ObjectID(np.random.bytes(20))
+        worker.current_task_id = ray.ObjectID(
+            np.random.bytes(ray_constants.ID_SIZE))
         # Reset the state of the numpy random number generator.
         np.random.set_state(numpy_state)
         # Set other fields needed for computing task IDs.
diff --git a/test/runtest.py b/test/runtest.py
index e8b099894..8e11adb4c 100644
--- a/test/runtest.py
+++ b/test/runtest.py
@@ -13,6 +13,7 @@ from collections import defaultdict, namedtuple, OrderedDict
 import numpy as np
 
 import ray
+import ray.ray_constants as ray_constants
 import ray.test.test_utils
 
 
@@ -2131,8 +2132,6 @@ class GlobalStateAPI(unittest.TestCase):
 
         self.assertEqual(ray.global_state.object_table(), {})
 
-        ID_SIZE = 20
-
         driver_id = ray.experimental.state.binary_to_hex(
             ray.worker.global_worker.worker_id)
         driver_task_id = ray.experimental.state.binary_to_hex(
@@ -2150,14 +2149,14 @@ class GlobalStateAPI(unittest.TestCase):
             self.assertEqual(task_table[driver_task_id]["TaskSpec"]["TaskID"],
                              driver_task_id)
             self.assertEqual(task_table[driver_task_id]["TaskSpec"]["ActorID"],
-                             ID_SIZE * "ff")
+                             ray_constants.ID_SIZE * "ff")
             self.assertEqual(task_table[driver_task_id]["TaskSpec"]["Args"],
                              [])
             self.assertEqual(
                 task_table[driver_task_id]["TaskSpec"]["DriverID"], driver_id)
             self.assertEqual(
                 task_table[driver_task_id]["TaskSpec"]["FunctionID"],
-                ID_SIZE * "ff")
+                ray_constants.ID_SIZE * "ff")
             self.assertEqual(
                 (task_table[driver_task_id]["TaskSpec"]["ReturnObjectIDs"]),
                 [])
@@ -2169,7 +2168,7 @@ class GlobalStateAPI(unittest.TestCase):
                 driver_task_id)
             self.assertEqual(
                 task_table[driver_task_id][0]["TaskSpec"]["ActorID"],
-                ID_SIZE * "ff")
+                ray_constants.ID_SIZE * "ff")
             self.assertEqual(task_table[driver_task_id][0]["TaskSpec"]["Args"],
                              [])
             self.assertEqual(
@@ -2177,7 +2176,7 @@ class GlobalStateAPI(unittest.TestCase):
                 driver_id)
             self.assertEqual(
                 task_table[driver_task_id][0]["TaskSpec"]["FunctionID"],
-                ID_SIZE * "ff")
+                ray_constants.ID_SIZE * "ff")
             self.assertEqual(
                 (task_table[driver_task_id][0]["TaskSpec"]["ReturnObjectIDs"]),
                 [])
@@ -2222,7 +2221,7 @@ class GlobalStateAPI(unittest.TestCase):
             task_spec = task_table[task_id]["TaskSpec"]
         else:
             task_spec = task_table[task_id][0]["TaskSpec"]
-        self.assertEqual(task_spec["ActorID"], ID_SIZE * "ff")
+        self.assertEqual(task_spec["ActorID"], ray_constants.ID_SIZE * "ff")
         self.assertEqual(task_spec["Args"], [1, "hi", x_id])
         self.assertEqual(task_spec["DriverID"], driver_id)
         self.assertEqual(task_spec["ReturnObjectIDs"], [result_id])