diff --git a/src/proofofwork.py b/src/proofofwork.py
index 5e157db9..eac21df0 100644
--- a/src/proofofwork.py
+++ b/src/proofofwork.py
@@ -19,6 +19,10 @@ import state
 import tr
 from bmconfigparser import config
 from debug import logger
+from defaults import (
+    networkDefaultProofOfWorkNonceTrialsPerByte,
+    networkDefaultPayloadLengthExtraBytes)
+
 
 bitmsglib = 'bitmsghash.so'
 bmpow = None
@@ -341,6 +345,28 @@ def run(target, initialHash):
         pass  # fallback
 
 
+def getTarget(payloadLength, ttl, nonceTrialsPerByte, payloadLengthExtraBytes):
+    """Get PoW target for given length, ttl and difficulty params"""
+    return 2 ** 64 / (
+        nonceTrialsPerByte * (
+            payloadLength + 8 + payloadLengthExtraBytes + ((
+                ttl * (
+                    payloadLength + 8 + payloadLengthExtraBytes
+                )) / (2 ** 16))
+        ))
+
+
+def calculate(
+    payload, ttl,
+    nonceTrialsPerByte=networkDefaultProofOfWorkNonceTrialsPerByte,
+    payloadLengthExtraBytes=networkDefaultPayloadLengthExtraBytes
+):
+    """Do the PoW for the payload and TTL with optional difficulty params"""
+    return run(getTarget(
+        len(payload), ttl, nonceTrialsPerByte, payloadLengthExtraBytes),
+        hashlib.sha512(payload).digest())
+
+
 def resetPoW():
     """Initialise the OpenCL PoW"""
     openclpow.initCL()
diff --git a/src/tests/samples.py b/src/tests/samples.py
index dd862318..55debea3 100644
--- a/src/tests/samples.py
+++ b/src/tests/samples.py
@@ -91,3 +91,12 @@ sample_privsigningkey_wif = \
     b'5K42shDERM5g7Kbi3JT5vsAWpXMqRhWZpX835M2pdSoqQQpJMYm'
 sample_privencryptionkey_wif = \
     b'5HwugVWm31gnxtoYcvcK7oywH2ezYTh6Y4tzRxsndAeMi6NHqpA'
+
+
+# PoW
+
+sample_pow_target = 54227212183
+sample_pow_initial_hash = unhexlify(
+    '3758f55b5a8d902fd3597e4ce6a2d3f23daff735f65d9698c270987f4e67ad590'
+    'b93f3ffeba0ef2fd08a8dc2f87b68ae5a0dc819ab57f22ad2c4c9c8618a43b3'
+)
diff --git a/src/tests/test_openclpow.py b/src/tests/test_openclpow.py
index 4770072e..d9ccbe2e 100644
--- a/src/tests/test_openclpow.py
+++ b/src/tests/test_openclpow.py
@@ -3,9 +3,12 @@ Tests for openclpow module
 """
 
 import unittest
+from binascii import hexlify
 
 from pybitmessage import openclpow, proofofwork
 
+from .samples import sample_pow_target, sample_pow_initial_hash
+
 
 class TestOpenClPow(unittest.TestCase):
     """
@@ -19,11 +22,8 @@ class TestOpenClPow(unittest.TestCase):
     @unittest.skipUnless(openclpow.enabledGpus, "No GPUs found / enabled")
     def test_openclpow(self):
         """Check the working of openclpow module"""
-        target_ = 54227212183
-        initialHash = (
-            "3758f55b5a8d902fd3597e4ce6a2d3f23daff735f65d9698c270987f4e67ad590"
-            "b93f3ffeba0ef2fd08a8dc2f87b68ae5a0dc819ab57f22ad2c4c9c8618a43b3"
-        ).decode("hex")
-        nonce = openclpow.do_opencl_pow(initialHash.encode("hex"), target_)
+        nonce = openclpow.do_opencl_pow(
+            hexlify(sample_pow_initial_hash), sample_pow_target)
         self.assertLess(
-            nonce - proofofwork.trial_value(nonce, initialHash), target_)
+            nonce - proofofwork.trial_value(nonce, sample_pow_initial_hash),
+            sample_pow_target)
diff --git a/src/tests/test_proofofwork.py b/src/tests/test_proofofwork.py
index e85174f0..db1d8317 100644
--- a/src/tests/test_proofofwork.py
+++ b/src/tests/test_proofofwork.py
@@ -1,13 +1,17 @@
 """
 Tests for proofofwork module
 """
+# pylint: disable=protected-access
 
 import hashlib
+import os
+import time
 import unittest
-from binascii import unhexlify
 from struct import pack, unpack
 
-from pybitmessage import proofofwork
+from pybitmessage import proofofwork, protocol
+
+from .samples import sample_pow_target, sample_pow_initial_hash
 
 
 class TestProofofwork(unittest.TestCase):
@@ -17,20 +21,26 @@ class TestProofofwork(unittest.TestCase):
     def setUpClass(cls):
         proofofwork.init()
 
-    def test_empty(self):
-        """just reproducing the empty test from proofofwork.init()"""
-        self.assertEqual(
-            proofofwork._doCPoW(2**63, ""), [6485065370652060397, 4])
+    def test_calculate(self):
+        """Ensure a calculated nonce has sufficient work for the protocol"""
+        TTL = 24 * 60 * 60
+        payload = pack('>Q', int(time.time() + TTL)) + os.urandom(166)
+        nonce = proofofwork.calculate(payload, TTL)[1]
+        self.assertTrue(
+            protocol.isProofOfWorkSufficient(pack('>Q', nonce) + payload))
+        # raise difficulty
+        nonce = proofofwork.calculate(payload, TTL, 2000, 2000)[1]
+        self.assertTrue(
+            protocol.isProofOfWorkSufficient(
+                pack('>Q', nonce) + payload, 2000, 2000,
+                int(time.time()) + TTL - 3600))
 
     def test_with_target(self):
         """Do PoW with parameters from test_openclpow and check the result"""
-        target = 54227212183
-        initialHash = unhexlify(
-            '3758f55b5a8d902fd3597e4ce6a2d3f23daff735f65d9698c270987f4e67ad590'
-            'b93f3ffeba0ef2fd08a8dc2f87b68ae5a0dc819ab57f22ad2c4c9c8618a43b3'
-        )
-        nonce = proofofwork._doCPoW(target, initialHash)[0]
-        trialValue, = unpack(
+        nonce = proofofwork._doCPoW(
+            sample_pow_target, sample_pow_initial_hash)[0]
+        trial_value, = unpack(
             '>Q', hashlib.sha512(hashlib.sha512(
-                pack('>Q', nonce) + initialHash).digest()).digest()[0:8])
-        self.assertLess((nonce - trialValue), target)
+                pack('>Q', nonce) + sample_pow_initial_hash
+            ).digest()).digest()[0:8])
+        self.assertLess((nonce - trial_value), sample_pow_target)