How Often Does Old Faithful Erupt?

Faithful and true: The guide to viewing Old Faithful and other Yellowstone geysers

Old Faithful is the most famous geyser in Yellowstone National Park, although it is neither the tallest of the park's 500 geysers nor the most regular. Even though it doesn't erupt at exact hourly intervals, it sprays into the air more frequently than any other park geyser, reaching heights of up to 184 feet.

How often does Old Faithful erupt?

Old Faithful erupts, on average, about 17 times daily. Even though it doesn't follow a strict timetable, the geyser is unique in that its eruptions can be predicted within 10 minutes 90 percent of the time. The time between eruptions varies from 60 to 110 minutes. If Old Faithful erupts for less than 2.5 minutes, the next event will be in roughly 68 minutes; if it lasts more than 2.5 minutes, there will be an approximate 94-minute interval before the next eruption. The geyser is influenced by pressure building up in a reservoir below the earth and is unaffected by the weather and seasons above the earth's crust, making it a reliable year-round event.

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Beat the crowds

With predictions of eruptions accurate within 10 minutes, summer crowds gather swiftly in Old Faithful's viewing areas. A limited amount of benches in the park's five viewing areas fill up quickly, but a horseshoe-shaped walkway means you'll usually get to see the eruption just by walking further down the trail and standing along the rail.

If you don't want to be shoulder to shoulder with other summer tourists, plan to see the geyser between dawn and 11 a.m. or between 6 p.m. and dusk. Stay at Yellowstone Inn or Yellowstone Lodge to be less than a half-mile walk from the geyser. Go in the off-season to experience a true winter wonderland. Stay at the Old Faithful Snow Lodge between December and March to have easy access to the geyser basin and experience the park on snowshoe, cross-country skis or snowcoach.

There's an app for that!

Whether you have an iPhone or Android device, you can download the park's Geysers app to get notifications when Old Faithful's eruption window is about to begin. The app notifies you 10 minutes ahead of time, giving you plenty of time to walk from nearby lodges to see the event. The Geysers app also has prediction times and notifications for other geysers in the park to help you make the most of your geyser viewing in the park.

Grand: The eruption window for this fountain geyser is plus or minus 90 minutes. It puts on a good show lasting for 8 to 12 minutes and shooting up to 200 feet high, making it the tallest predictable geyser in the world. Two nearby geysers, Vent and Turban, are connected and erupt nearly in unison with Grand. The time between eruptions averages 6 hours and 45 minutes.

Castle: This 75-foot geyser erupts only every 13.5 hours or so. When it does, its 60- to 90-foot fountain lasts for 15 to 20 minutes. Castle isn't always predictable. Minor eruptions of 11 minutes signal violent splashing that lasts for hours without developing into a major eruption. It won't be predictable again until its next major eruption happens.

Great Fountain spurts up to 220 feet high for an hour or two at a time. The geyser erupts every 9 to 15 hours and is calm between eruptions. Just before an eruption, water begins bubbling out of the geyser's vent with violent bubbling about 3 feet tall. The pool then goes silent, and a giant bubble might form over it before the dramatic explosion of water. The geyser is 10 miles from Old Faithful, and its eruptions are predicted from Memorial Day through September.

Daisy is a cone geyser that sprays off at an angle about 75 feet into the air. The unique display lasts only 3.5 minutes, but you can catch it every 150 to 200 minutes with an eruption window of plus or minus 30 minutes.

Riverside is predictable within 30 minutes. It's 75-foot plume sprays for about 20 minutes. After an eruption, it takes the geyser 5.5 to 7 hours to rebuild pressure before the next one. You can tell when an eruption is imminent. About 2 hours before it spews, water overflows from its lower vent into the river. After another hour, water bubbles out of its upper vent. When the bubbling water from the upper vent spurts into the river, an eruption begins.