RootMetrics found Verizon's 4G upload and download speeds significantly higher than other carriers'.

Have you been wondering if that new 4G smartphone you purchased is really getting 4G speeds? Wonder no longer.

RootMetrics performed an extensive study to determine how each network’s 4G speeds are really holding up to their claims.

Their findings showed that Verizon’s LTE network performed with a 100% data success rate. Its average data speeds were between 4 and 14.5 times faster than competitors, and average upload speeds were between 4.7 and 49.3 times faster.

The testing was performed across the Seattle area.

The phone models tested included the HTC Thunderbolt (T-Mobile), HTC Inspire (AT&T), HTC Evo (Sprint), and Samsung Galaxy S (Verizon) . RootMetrics’ CEO Paul Griff said that the smartphone model and its hardware had very little to do with 4G performance — that is almost all network related.

Wired has previously broken down what each carrier means by “4G”, and what speeds should be expected from each service. Verizon’s LTE network promises speeds of 5-12 Mbps down and 1-5 Mbps up; AT&T’s HSPA+ network should provide 6Mbps down (and they plan to upgrade to LTE in 2011); Sprint’s WiMax technology promises an average of 3-6 Mbps down and 0.6-1.4 Mbps up; and T-Mobile’s HSPA+ is supposed to provide 5-10 Mbps down. AT&T has reportedly been capping 4G speeds on Android handsets, but this has not been definitively verified.

Over in Oakland, CA, the folks at TechnoBuffalo decided to perform a 4G speed test of their own using the HTC Inspire and Thunderbolt.

Using SpeedTest.net’s services and the phones’ Wi-Fi hotspot modes, they discovered median speeds of 8.85 Mbps down and 3.68 up on Verizon’s LTE network, and 2.16 Mbps down and .16 up on AT&T’s HSPA+ service — on par with RootMetrics’ results.

RootMetrics was careful to point out that merely achieving high data speeds doesn’t mean much unless it happens on a regular basis, though. It found that Verizon’s 4G download speeds were greater than 10 Mbps about 90% of the time, and their upload speeds were between 5 and 10 Mbps 100% of the time.

And Verizon’s average upload speeds were faster than every other carrier’s average download speeds by 37%.

A graph of how often each 4G service achieved a certain range of download speeds (from 0-500Kbps to greater than 10Mbps) shows Verizon dominating the high end, AT&T spending most of its time in the lower half, and Sprint and T-Mobile’s services ranging widely throughout.

How will AT&T and T-Mobile’s recently announced merger affect their 4G services? That’s yet to be seen.

“Our results stand alone and provide interesting context around consumer data experience for both carrier’s networks in the Seattle area,” says a representative from RootMetrics.

Until it is known how and if the two carriers will combine their networks, it’s difficult to say how the merger will affect their future 4G service. But it’s safe to say, unless it’s LTE, it won’t hold a candle to Verizon’s network.

Comparing the Carriers: 4G Data Speed Study (.pdf) [Thanks Julie!]