Starbucks customers in the U.S. ordering iced drinks will soon be able to dose up on nearly a litre as the Seattle-based company launches its biggest drink size yet.

At 920 millilitres (31 ounces) the Trenta is just over 200 millilitres (7 ounces) more than the company's current largest drink size — the Venti.

The Trenta will be exclusively for iced coffee, iced tea and iced lemonade, Seattle-based Starbucks told Reuters on Sunday.

The name follows the Starbucks tradition of using Italian words instead of plain sizes such as small, medium and large. Trenta is Italian for 30.

Fast-food restaurants and convenience stores have long been "super-sizing" their portions, including drink sizes. The 7-Eleven convenience store chain for example offers one of the biggest drinks with its line of Big Gulp sizes. They range from 945 ml to 1.9 litres.

Starbuck's Trenta will cost an extra 50 cents over Venti sizes and will be available in all of its U.S. coffee shops by May 3. It will roll out in 14 states, including Virginia, Georgia and Arizona on Jan. 18 and in California on Feb. 1.

A Starbucks spokesperson said the new size was tested in March 2010 in Phoenix, Ariz., and Tampa, Fla. in response to customers who said they would like larger sizes.

The company said unsweetened Trenta drinks will have fewer than 90 calories and that sweetened versions will have less than 230 calories.