--- a/src/java.base/share/classes/java/util/concurrent/TimeUnit.java	Fri Jun 08 11:04:58 2018 -0700
+++ b/src/java.base/share/classes/java/util/concurrent/TimeUnit.java	Fri Jun 08 11:38:40 2018 -0700
@@ -35,6 +35,7 @@
 
 package java.util.concurrent;
 
+import java.time.Duration;
 import java.time.temporal.ChronoUnit;
 import java.util.Objects;
 
@@ -192,6 +193,50 @@
     }
 
     /**
+     * Converts the given time duration to this unit.
+     *
+     * <p>For any TimeUnit {@code unit},
+     * {@code unit.convert(Duration.ofNanos(n))}
+     * is equivalent to
+     * {@code unit.convert(n, NANOSECONDS)}, and
+     * {@code unit.convert(Duration.of(n, unit.toChronoUnit()))}
+     * is equivalent to {@code n} (in the absence of overflow).
+     *
+     * @param duration the time duration
+     * @return the converted duration in this unit,
+     * or {@code Long.MIN_VALUE} if conversion would negatively overflow,
+     * or {@code Long.MAX_VALUE} if it would positively overflow.
+     * @throws NullPointerException if {@code duration} is null
+     * @see Duration#of(long,TemporalUnit)
+     * @since 11
+     */
+    public long convert(Duration duration) {
+        long secs = duration.getSeconds();
+        int nano = duration.getNano();
+        if (secs < 0 && nano > 0) {
+            // use representation compatible with integer division
+            secs++;
+            nano -= SECOND_SCALE;
+        }
+        final long s, nanoVal;
+        // Optimize for the common case - NANOSECONDS without overflow
+        if (this == NANOSECONDS)
+            nanoVal = nano;
+        else if ((s = scale) < SECOND_SCALE)
+            nanoVal = nano / s;
+        else if (this == SECONDS)
+            return secs;
+        else
+            return secs / secRatio;
+        long val = secs * secRatio + nanoVal;
+        return ((secs < maxSecs && secs > -maxSecs) ||
+                (secs == maxSecs && val > 0) ||
+                (secs == -maxSecs && val < 0))
+            ? val
+            : (secs > 0) ? Long.MAX_VALUE : Long.MIN_VALUE;
+    }
+
+    /**
      * Equivalent to
      * {@link #convert(long, TimeUnit) NANOSECONDS.convert(duration, this)}.
      * @param duration the duration
@@ -221,10 +266,8 @@
      */
     public long toMicros(long duration) {
         long s, m;
-        if ((s = scale) == MICRO_SCALE)
-            return duration;
-        else if (s < MICRO_SCALE)
-            return duration / microRatio;
+        if ((s = scale) <= MICRO_SCALE)
+            return (s == MICRO_SCALE) ? duration : duration / microRatio;
         else if (duration > (m = maxMicros))
             return Long.MAX_VALUE;
         else if (duration < -m)
@@ -243,10 +286,8 @@
      */
     public long toMillis(long duration) {
         long s, m;
-        if ((s = scale) == MILLI_SCALE)
-            return duration;
-        else if (s < MILLI_SCALE)
-            return duration / milliRatio;
+        if ((s = scale) <= MILLI_SCALE)
+            return (s == MILLI_SCALE) ? duration : duration / milliRatio;
         else if (duration > (m = maxMillis))
             return Long.MAX_VALUE;
         else if (duration < -m)
@@ -265,10 +306,8 @@
      */
     public long toSeconds(long duration) {
         long s, m;
-        if ((s = scale) == SECOND_SCALE)
-            return duration;
-        else if (s < SECOND_SCALE)
-            return duration / secRatio;
+        if ((s = scale) <= SECOND_SCALE)
+            return (s == SECOND_SCALE) ? duration : duration / secRatio;
         else if (duration > (m = maxSecs))
             return Long.MAX_VALUE;
         else if (duration < -m)

--- a/test/jdk/java/util/concurrent/tck/TimeUnit8Test.java	Fri Jun 08 11:04:58 2018 -0700
+++ b/test/jdk/java/util/concurrent/tck/TimeUnit8Test.java	Fri Jun 08 11:38:40 2018 -0700
@@ -40,8 +40,12 @@
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
 
+import java.time.Duration;
 import java.time.temporal.ChronoUnit;
+import java.util.Arrays;
+import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
+import java.util.stream.LongStream;
 
 import junit.framework.Test;
 import junit.framework.TestSuite;
@@ -100,4 +104,85 @@
         }
     }
 
+    /**
+     * convert(Duration) roundtrips with Duration.ofXXXX and Duration.of(long, ChronoUnit)
+     */
+    public void testConvertDuration_roundtripDurationOf() {
+        long n = ThreadLocalRandom.current().nextLong();
+
+        assertEquals(n, NANOSECONDS.convert(Duration.ofNanos(n)));
+        assertEquals(n, NANOSECONDS.convert(Duration.of(n, ChronoUnit.NANOS)));
+        assertEquals(n, MILLISECONDS.convert(Duration.ofMillis(n)));
+        assertEquals(n, MILLISECONDS.convert(Duration.of(n, ChronoUnit.MILLIS)));
+        assertEquals(n, SECONDS.convert(Duration.ofSeconds(n)));
+        assertEquals(n, SECONDS.convert(Duration.of(n, ChronoUnit.SECONDS)));
+        n /= 60;
+        assertEquals(n, MINUTES.convert(Duration.ofMinutes(n)));
+        assertEquals(n, MINUTES.convert(Duration.of(n, ChronoUnit.MINUTES)));
+        n /= 60;
+        assertEquals(n, HOURS.convert(Duration.ofHours(n)));
+        assertEquals(n, HOURS.convert(Duration.of(n, ChronoUnit.HOURS)));
+        n /= 24;
+        assertEquals(n, DAYS.convert(Duration.ofDays(n)));
+        assertEquals(n, DAYS.convert(Duration.of(n, ChronoUnit.DAYS)));
+    }
+
+    /**
+     * convert(Duration.ofNanos(n)) agrees with convert(n, NANOSECONDS)
+     */
+    public void testConvertDuration_roundtripDurationOfNanos() {
+        // Test values near unit transitions and near overflow.
+        LongStream.concat(
+                Arrays.stream(TimeUnit.values()).mapToLong(u -> u.toNanos(1)),
+                LongStream.of(Long.MAX_VALUE, Long.MIN_VALUE))
+            .flatMap(n -> LongStream.of(n, n + 1, n - 1))
+            .flatMap(n -> LongStream.of(n, n + 1_000_000_000, n - 1_000_000_000))
+            .flatMap(n -> LongStream.of(n, -n))
+            // .peek(System.err::println)
+            .forEach(n -> Arrays.stream(TimeUnit.values()).forEach(
+                u -> assertEquals(u.convert(n, NANOSECONDS),
+                                  u.convert(Duration.ofNanos(n)))));
+    }
+
+    /**
+     * convert(Duration) doesn't misbehave near Long.MAX_VALUE and Long.MIN_VALUE.
+     */
+    public void testConvertDuration_nearOverflow() {
+        ChronoUnit NANOS = ChronoUnit.NANOS;
+        Duration maxDuration = Duration.ofSeconds(Long.MAX_VALUE, 999_999_999);
+        Duration minDuration = Duration.ofSeconds(Long.MIN_VALUE, 0);
+
+        for (TimeUnit u : TimeUnit.values()) {
+            ChronoUnit cu = u.toChronoUnit();
+            long r;
+            if (u.toNanos(1) > SECONDS.toNanos(1)) {
+                r = u.toNanos(1) / SECONDS.toNanos(1);
+
+                assertThrows(ArithmeticException.class,
+                             () -> Duration.of(Long.MAX_VALUE, cu),
+                             () -> Duration.of(Long.MIN_VALUE, cu));
+            } else {
+                r = 1;
+
+                Duration max = Duration.of(Long.MAX_VALUE, cu);
+                Duration min = Duration.of(Long.MIN_VALUE, cu);
+                assertEquals(Long.MAX_VALUE, u.convert(max));
+                assertEquals(Long.MAX_VALUE - 1, u.convert(max.minus(1, NANOS)));
+                assertEquals(Long.MAX_VALUE - 1, u.convert(max.minus(1, cu)));
+                assertEquals(Long.MIN_VALUE, u.convert(min));
+                assertEquals(Long.MIN_VALUE + 1, u.convert(min.plus(1, NANOS)));
+                assertEquals(Long.MIN_VALUE + 1, u.convert(min.plus(1, cu)));
+                assertEquals(Long.MAX_VALUE, u.convert(max.plus(1, NANOS)));
+                if (u != SECONDS) {
+                    assertEquals(Long.MAX_VALUE, u.convert(max.plus(1, cu)));
+                    assertEquals(Long.MIN_VALUE, u.convert(min.minus(1, NANOS)));
+                    assertEquals(Long.MIN_VALUE, u.convert(min.minus(1, cu)));
+                }
+            }
+
+            assertEquals(Long.MAX_VALUE / r, u.convert(maxDuration));
+            assertEquals(Long.MIN_VALUE / r, u.convert(minDuration));
+        }
+    }
+
 }