(CNN) Catastrophic flooding has swallowed swaths of Louisiana in a deluge that the governor calls " unprecedented ." But the breadth of the destruction can be hard to imagine.

Here's what the calamity looks like, by the numbers:

60,000: Homes damaged

Ryan Evans walks along a flooded road on August 15 in Baton Rouge, Louisiana.

More than 60,000 homes have been reported damaged by Louisiana parishes impacted by the flooding, said Mike Steele, the communications director for the Louisiana Governor's Office of Homeland Security and Emergency Preparedness. However, the damage may be much greater. Steele says a forthcoming assessment by FEMA will be more thorough.

Gov. John Bel Edwards said Tuesday that volunteers are needed to help clean out mud from homes.

"Not everyone can do this on their own," the governor said. He said anyone interested in helping can visit VolunteerLouisiana.gov

The entire state of Louisiana has just 4.6 million people -- less than the population of metro Atlanta.

6,900,000,000,000: Gallons of rainfall in one week

About 6.9 trillion gallons of rain pummeled Louisiana between August 8 and 14, according to meteorologist Ryan Maue.

That's enough to fill more than 10.4 million Olympic-size swimming pools.

13: Deaths across the state

A boat motors between flooded homes after torrential rainfail in Hammond, Louisiana.

Officials have reported five in East Baton Rouge Parish, three in Tangipahoa Parish, two in St. Helena Parish, two in Livingston Parish, and one in Rapides Parish.

$30 million: The estimated cost of the flood so far

"This disaster is the worst to hit the United States since Superstorm Sandy, and we anticipate it will cost at least $30 million -- a number which may grow as we learn more about the scope and magnitude of the devastation," Red Cross official Brad Kieserman said.

The costliest US floods Hurricane Katrina in 2005: $16.3 billion Superstorm Sandy in 2012: $8.3 billion Hurricane Ike in 2008: $2.7 billion Hurricane Ivan in 2004: $1.6 billion Hurricane Irene in 2011: $1.3 billion Source: Federal Emergency Management Agency

31.39: Inches of rain in one day

Residents grapple with epic flooding in Livingston Parish, Louisiana.

More than 2 1/2 feet of rain pummeled part of Livingston Parish on Tuesday, the National Oceanic and Atmospheric Administration said.

The hardest-hit part of the parish was Watson, where 31.39 inches fell between 6 a.m. and 9 p.m. Tuesday.

Baton Rouge was pounded with more than 19 inches of rain during those same 15 hours.

20,000: People rescued

Members of the Coast Guard and National Guard, along with emergency responders and regular civilians, helped take more than 20,000 residents to safety, officials said.

Gov. Edwards said 1,000 pets have also been rescued.

Ann Chapman from the Louisiana State Animal Response Team carries a dog she helped rescue in Baton Rouge.

500 years: Expected frequency of a flood this big

A man navigates a boat of rescued goats in Gonzales, Louisiana.

The likelihood of a flood this catastrophic in the Baton Rouge area is about once every 500 years.

Since last August, five other floods across the country have been considered "500-year floods," according to data from the National Oceanic and Atmospheric Administration.

14.9 feet: Level of Amite River on Wednesday

For three consecutive days, the Amite River at Port Vincent broke the previous record level of 14.6 feet. After cresting at 17.45 feet early Monday, the river stood at 14.9 feet Wednesday.

Cars stranded on Hwy 16 north of Port Vincent, La. right now in chopper #laflood pic.twitter.com/8is5IowJXc — Maya Lau (@mayalau) August 15, 2016

12: Parishes declared as disaster areas

Rescuers move cattle across a flooded street to dry land in Sorrento, Louisiana.

President Barack Obama has granted Edwards' request for an emergency declaration in 12 parishes, the governor said Tuesday.

Edwards said he expects that number to rise, as he has requested emergency declarations in more than a dozen other parishes as well.

106,000: Households registered with FEMA

More than 106,000 individuals and households have registered with FEMA for assistance as survivors are in need of temporary rental help, essential home repairs and other disaster-related needs. More than $55 million has been approved to help survivors.