WHAT YOU NEED TO KNOW
Area code 303 serves the Denver metro area in Colorado, including Denver, Boulder, Lakewood, and Arvada. Established in 1947 as one of the original NANP codes covering all of Colorado, it now focuses on the Denver metro region. The code covers approximately 3 million residents and shares coverage with overlay code 720.
- Population: ~3.0 million residents in the metro
- Overlay: Overlay: 720 (added in 1998)
- Dialing: 10-digit dialing required
- Source Type: Local geographic code
Geographic Coverage
Area code 303 covers the Denver-Aurora metro area, spanning multiple counties including Denver, Jefferson, Arapahoe, Boulder, Adams, Douglas, and Broomfield. Key cities include Denver, Boulder, Lakewood, Arvada, Westminster, Thornton, Highlands Ranch, Centennial, Littleton, Englewood, Golden, Broomfield, Castle Rock, Parker, and Longmont. The code does not cover all of Colorado; the remainder of the state falls under area code 970, which was split off in 1995.
Population and Business Context
The Denver metro market covered by area code 303 is one of the fastest-growing in the United States. Major industries include aerospace and defense, technology, financial services, healthcare, and energy. The region is home to Fortune 500 companies, a strong startup ecosystem, and the University of Colorado system. Denver serves as a regional hub for the Mountain West, drawing significant business and commercial activity across the front range.
Area Code History
Area code 303 was assigned in 1947 as part of the original North American Numbering Plan, at which time it covered the entire state of Colorado. In 1995, Colorado's rapid population growth prompted a split: the eastern plains and western slope areas were moved to the new 970 area code, concentrating 303 on the Denver metro and adjacent front range counties. In 1998, area code 720 was introduced as an overlay to address growing demand for new phone numbers within the same geographic region.
How to Dial
Callers within the 303 and 720 overlay region must use 10-digit dialing, meaning you must dial all 10 digits (area code plus 7-digit number) for every local call. This rule has been in effect since the 720 overlay was introduced. No leading 1 is required for local calls within the overlay area, but long-distance calls outside the region follow the standard 1 plus 10-digit format. Callers from outside Colorado should dial 1-303 followed by the 7-digit number.
Need a 303 Number for Your Denver Metro Business?
Businesses operating in the Denver metro area can establish a local presence with a 303 tracking number through Convirza. Convirza provisions trackable local numbers in any North American area code, including 303 and its overlay 720, so your business appears local to Denver, Boulder, Lakewood, and surrounding communities. Setup takes minutes and works alongside your existing phone system. Every call to your 303 number is automatically scored, recorded, and source-attributed using dynamic number insertion (DNI). You can route calls to any team member or location, track which marketing campaigns drive phone leads, and access detailed call analytics in one dashboard. No guesswork - just clear data on what is generating calls in the Denver market.
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