Distance: 7.8 miles (12.5 km) round trip to Dewey Point;
9.2 miles (14.7 km) for Dewey Point plus Crocker Point;
10.5 miles (16.8 km) for Dewey, Crocker, and Stanford Points
Elevation at trailhead: 6,900 feet (2,100 meters)
Dewey Point Elevation: 7,200 feet (2,200 meters)
Crocker Point Elevation: 7,100 feet (2,160 meters)
Stanford Point Elevation: 6,659 feet (2,030 meters)
The red line shows the route from the trailhead at Glacier Point Road to Dewey Point. This stretch is just under 4 miles (6.5 km) long and has little elevation gain.
The blue line shows the bonus stretch from Dewey Point to Crocker and Stanford Points; the blue balloons mark the locations, from left to right, of Stanford, Crocker, and Dewey Points. This section of the trail is a little under 1.5 miles (2.5 km) long and descends 540 feet (165 meters).
The green lines mark the Pohono Trail, which merges with this trail about two miles past the trailhead. If you continue westward from Stanford Point along the Pohono Trail, you'll pass Inspiration Point and eventually arrive at the Tunnel View. If you take it east from its intersection with the Dewey Point Trail, you'll pass Taft Point and Sentinel Dome and end up nearly 6 miles (10 km) later at Glacier Point, where you should feel entitled to buy out as much of the cafeteria's ice cream as you can carry, though you may want to save some of your money to help persuade someone to drive you the 8 miles or so back to the Dewey Point trailhead.
The stretch of the Pohono Trail west of Stanford Point descends 2,600 feet (800 meters); the eastern stretch involves a few hundred feet of ascent to the base of Sentinel Dome before descending again to Glacier Point, but is mostly level otherwise.
You'll also go through McGurk Meadow at the mile mark of this hike. You can see the meadow clearing by zooming in on the green marker.