diff --git a/apps/bmv2-demo/wcmp/src/main/java/org/onosproject/bmv2/demo/app/wcmp/WcmpGroupTreatmentBuilder.java b/apps/bmv2-demo/wcmp/src/main/java/org/onosproject/bmv2/demo/app/wcmp/WcmpGroupTreatmentBuilder.java
new file mode 100644
index 0000000..731b2ca
--- /dev/null
+++ b/apps/bmv2-demo/wcmp/src/main/java/org/onosproject/bmv2/demo/app/wcmp/WcmpGroupTreatmentBuilder.java
@@ -0,0 +1,136 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.bmv2.demo.app.wcmp;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import org.onlab.util.ImmutableByteSequence;
+import org.onosproject.bmv2.api.runtime.Bmv2Action;
+import org.onosproject.bmv2.api.runtime.Bmv2ExtensionTreatment;
+import org.onosproject.bmv2.api.utils.Bmv2TranslatorUtils;
+import org.onosproject.net.DeviceId;
+import org.onosproject.net.PortNumber;
+import org.onosproject.net.flow.instructions.ExtensionTreatment;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static java.util.stream.Collectors.toList;
+import static org.onosproject.bmv2.api.utils.Bmv2TranslatorUtils.fitByteSequence;
+import static org.onosproject.bmv2.demo.app.wcmp.WcmpFabricApp.WCMP_CONTEXT;
+import static org.onosproject.bmv2.demo.app.wcmp.WcmpInterpreter.*;
+
+/**
+ * Builder of WCMP extension treatment.
+ */
+public final class WcmpGroupTreatmentBuilder {
+
+    private static final double MAX_ERROR = 0.0001;
+
+    private static final Map<DeviceId, Map<Map<PortNumber, Double>, Integer>> DEVICE_GROUP_ID_MAP = Maps.newHashMap();
+
+    private int groupId;
+
+    /**
+     * Sets the WCMP group ID.
+     *
+     * @param groupId an integer value
+     * @return this
+     */
+    public WcmpGroupTreatmentBuilder withGroupId(int groupId) {
+        this.groupId = groupId;
+        return this;
+    }
+
+    /**
+     * Returns a new extension treatment.
+     *
+     * @return an extension treatment
+     */
+    public ExtensionTreatment build() {
+        checkArgument(groupId >= 0, "group id must be a non-zero positive integer");
+        ImmutableByteSequence groupIdBs = ImmutableByteSequence.copyFrom(groupId);
+        final int groupIdBitWidth = WCMP_CONTEXT.configuration().headerType(WCMP_META_T).field(GROUP_ID).bitWidth();
+        try {
+            groupIdBs = fitByteSequence(groupIdBs, groupIdBitWidth);
+            return new Bmv2ExtensionTreatment(
+                    Bmv2Action.builder()
+                            .withName(WCMP_GROUP)
+                            .addParameter(groupIdBs)
+                            .build());
+        } catch (Bmv2TranslatorUtils.ByteSequenceFitException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public static int groupIdOf(DeviceId did, Map<PortNumber, Double> weightedPorts) {
+        DEVICE_GROUP_ID_MAP.putIfAbsent(did, Maps.newHashMap());
+        // Counts the number of unique portNumber sets for each device ID.
+        // Each distinct set of portNumbers will have a unique ID.
+        return DEVICE_GROUP_ID_MAP.get(did).computeIfAbsent(weightedPorts,
+                                                            (pp) -> DEVICE_GROUP_ID_MAP.get(did).size() + 1);
+    }
+
+    public static List<Integer> toPrefixLengths(List<Double> weigths) throws WcmpGroupException {
+
+        double weightSum = weigths.stream()
+                .mapToDouble(Double::doubleValue)
+                .map(WcmpGroupTreatmentBuilder::roundDouble)
+                .sum();
+
+        if (Math.abs(weightSum - 1) > MAX_ERROR) {
+            throw new WcmpGroupException("weights sum is expected to be 1, found was " + weightSum);
+        }
+
+        final int selectorBitWidth = WCMP_CONTEXT.configuration().headerType(WCMP_META_T).field(SELECTOR).bitWidth();
+        final int availableBits = selectorBitWidth - 1;
+
+        List<Long> prefixDiffs = weigths.stream().map(w -> Math.round(w * availableBits)).collect(toList());
+
+        final long bitSum = prefixDiffs.stream().mapToLong(Long::longValue).sum();
+        final long error = availableBits - bitSum;
+
+        if (error != 0) {
+            // Lazy intuition here is that the error can be absorbed by the longest prefixDiff with the minor impact.
+            Long maxDiff = Collections.max(prefixDiffs);
+            int idx = prefixDiffs.indexOf(maxDiff);
+            prefixDiffs.remove(idx);
+            prefixDiffs.add(idx, maxDiff + error);
+        }
+        List<Integer> prefixLengths = Lists.newArrayList();
+
+        int prefix = 1;
+        for (Long p : prefixDiffs) {
+            prefixLengths.add(prefix);
+            prefix += p;
+        }
+        return ImmutableList.copyOf(prefixLengths);
+    }
+
+    private static double roundDouble(double n) {
+        // 5 digits precision.
+        return (double) Math.round(n * 100000d) / 100000d;
+    }
+
+    public static class WcmpGroupException extends Exception {
+        public WcmpGroupException(String s) {
+        }
+    }
+}