diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/ClientCookieEncoder.java b/codec-http/src/main/java/io/netty/handler/codec/http/ClientCookieEncoder.java
index 178dbdb64f..1f840e00af 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/ClientCookieEncoder.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/ClientCookieEncoder.java
@@ -42,7 +42,7 @@ public final class ClientCookieEncoder {
             throw new NullPointerException("cookie");
         }
 
-        StringBuilder buf = new StringBuilder();
+        StringBuilder buf = new StringBuilder(estimateClientLength(cookie));
         encode(buf, cookie);
         return stripTrailingSeparator(buf);
     }
@@ -52,7 +52,16 @@ public final class ClientCookieEncoder {
             throw new NullPointerException("cookies");
         }
 
-        StringBuilder buf = new StringBuilder();
+        int initialCapacity = 0;
+        for (Cookie c: cookies) {
+            if (c == null) {
+                break;
+            }
+
+            initialCapacity += estimateClientLength(c);
+        }
+
+        StringBuilder buf = new StringBuilder(initialCapacity);
         for (Cookie c: cookies) {
             if (c == null) {
                 break;
@@ -68,7 +77,16 @@ public final class ClientCookieEncoder {
             throw new NullPointerException("cookies");
         }
 
-        StringBuilder buf = new StringBuilder();
+        int initialCapacity = 0;
+        for (Cookie c: cookies) {
+            if (c == null) {
+                break;
+            }
+
+            initialCapacity += estimateClientLength(c);
+        }
+
+        StringBuilder buf = new StringBuilder(initialCapacity);
         for (Cookie c: cookies) {
             if (c == null) {
                 break;
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/CookieEncoderUtil.java b/codec-http/src/main/java/io/netty/handler/codec/http/CookieEncoderUtil.java
index 66e24a9d34..c57e00caa7 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/CookieEncoderUtil.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/CookieEncoderUtil.java
@@ -25,6 +25,77 @@ final class CookieEncoderUtil {
         return buf.toString();
     }
 
+    static int estimateClientLength(Cookie c) {
+        int estimate = estimateLength(c.getName(), c.getValue());
+
+        if (c.getPath() != null) {
+            estimate += estimateLength(CookieHeaderNames.PATH, c.getPath());
+        }
+
+        if (c.getDomain() != null) {
+            estimate += estimateLength(CookieHeaderNames.DOMAIN, c.getDomain());
+        }
+
+        if (c.getVersion() > 0) {
+            estimate += 12; // '$Version=N; '
+            int numPorts = c.getPorts().size();
+            if (numPorts > 0) {
+                estimate += 10; // '$Port=""; '
+                estimate += numPorts * 4;
+            }
+        }
+
+        return estimate;
+    }
+
+    static int estimateServerLength(Cookie c) {
+        int estimate = estimateLength(c.getName(), c.getValue());
+
+        if (c.getMaxAge() != Long.MIN_VALUE) {
+            estimate += 41; // 'Expires=Sun, 06 Nov 1994 08:49:37 +0900; '
+        }
+
+        if (c.getPath() != null) {
+            estimate += estimateLength(CookieHeaderNames.PATH, c.getPath());
+        }
+
+        if (c.getDomain() != null) {
+            estimate += estimateLength(CookieHeaderNames.DOMAIN, c.getDomain());
+        }
+        if (c.isSecure()) {
+            estimate += 8; // 'Secure; '
+        }
+        if (c.isHttpOnly()) {
+            estimate += 10; // 'HTTPOnly; '
+        }
+        if (c.getVersion() > 0) {
+            estimate += 11; // 'Version=N; '
+            if (c.getComment() != null) {
+                estimate += estimateLength(CookieHeaderNames.COMMENT, c.getComment());
+            }
+
+            if (c.getCommentUrl() != null) {
+                estimate += estimateLength(CookieHeaderNames.COMMENTURL, c.getCommentUrl());
+            }
+
+            int numPorts = c.getPorts().size();
+            if (numPorts > 0) {
+                estimate += 9; // 'Port=""; '
+                estimate += numPorts * 4;
+            }
+
+            if (c.isDiscard()) {
+                estimate += 9; // 'Discard; '
+            }
+        }
+
+        return estimate;
+    }
+
+    private static int estimateLength(String name, String value) {
+        return name.length() + value.length() + 6;
+    }
+
     static void add(StringBuilder sb, String name, String val) {
         if (val == null) {
             addQuoted(sb, name, "");
diff --git a/codec-http/src/main/java/io/netty/handler/codec/http/ServerCookieEncoder.java b/codec-http/src/main/java/io/netty/handler/codec/http/ServerCookieEncoder.java
index f46176606b..c7f724c428 100644
--- a/codec-http/src/main/java/io/netty/handler/codec/http/ServerCookieEncoder.java
+++ b/codec-http/src/main/java/io/netty/handler/codec/http/ServerCookieEncoder.java
@@ -47,7 +47,7 @@ public final class ServerCookieEncoder {
             throw new NullPointerException("cookie");
         }
 
-        StringBuilder buf = new StringBuilder();
+        StringBuilder buf = new StringBuilder(estimateServerLength(cookie));
 
         add(buf, cookie.getName(), cookie.getValue());