Even though Apple doesn't break down sales figures for specific iPhone devices, a new study suggests that the record-breaking sales of the iPhone lineup are mainly driven by the 4.7-inch device, not the 5.5-inch iPhone 6 Plus.

The sales breakdown, released by Consumer Intelligence Research Partners, applies to the first 30 days of iPhone 6 and iPhone 6 Plus availability in the U.S.

USB analyst Steven Milunovich mentioned in a summary of the breakdown that the iPhone 6 accounted for approximately 68 percent of all iPhone sales. The iPhone 6 Plus accounted for around 23 and 24 percent, according to the summary.

The new iPhones represented nearly 91 percent of total iPhone sales during their first four weeks of availability, with the remaining units represented by last year's iPhone 5s and iPhone 5c devices.

In 2013, Milunovich revealed that the iPhone 5s and iPhone 5c accounted for 84 percent of total iPhone sales after just one month. This means customers are more intrigued by the latest Apple premium models this year.

Milunovich said that though sales for the iPhone 6 is beating iPhone 6 Plus sales by a 3-to-1 margin, it's difficult to tell how strong the demand is for the bigger option, since Apple continues to face production shortages for the huge device.

CIRP's research also analyzed capacity, and determined that the average storage capacity for buyers was approximately 48 gigabytes, which is nearly double the average storage capacity from last year.

This year, Apple got rid of the 32-gigabyte capacity, and currently offers the iPhone 6 Plus in sizes of 16, 64, and 128 gigabytes, according to Apple.com.

A number of investors think that customers will upgrade to the more expensive 64- and 128-gig options in 2014, which would boost Apple's margins. The iPhone 6 Plus also carries a $100 premium over iPhone 6 models, which should help pad Apple's bottom line, according to AppleInsider.

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