When San Francisco city officials explain why their annual budgets are so huge — this year’s totals $9.6 billion, an all-time record — there are usually two explanations.

First, new residents are swarming into San Francisco like seagulls to AT&T Park, and they’re expensive. The new residents, not the seagulls. The second? We’re a city and a county, which means we’re responsible for just about everything.

But on closer inspection, neither explanation holds up completely. For starters, the city budget has soared in recent years, far outpacing the population growth.

In 2010, the budget totaled $6.4 billion in a city with 805,000 people, meaning the city spent nearly $8,000 per capita. Six years later, the $9.6 billion budget is paying for services for 865,000 residents, or $11,100 per capita. Inflation explains a little of that increase, but certainly not all of it.

When comparing San Francisco with other cities that also serve as counties, the explanation falls a little flat, as well. As a city, San Francisco pays for services like libraries, parks and police. As a county, it pays for services like the Sheriff’s Department, jails and public health.

Still, the $11,100 per capita annual spending here dwarfs the per capita spending in places with similar governance.

Philadelphia’s budget this year totals $4.2 billion for a population nearly twice the size of San Francisco’s. Denver will spend about $3 billion for a population approaching 700,000 people. The city and county of Honolulu, which pays for services for everybody on the island of Oahu in Hawaii, has a budget of $2.33 billion for a population close to 1 million people.

Of course, not every city offers the same services, so making exact comparisons is impossible. The good folks in Honolulu’s City Hall (we hereby volunteer to go there in person to do more research, editors) informed us their budget doesn’t pay for the airport or municipal hospital. The San Francisco budget does. Landlocked Denver, of course, wouldn’t have the port costs that San Francisco does.

Tracy Gordon is a senior fellow at the Urban-Brookings Tax Policy Center who specializes in the fiscal challenges of state and local governments. She said it surprised her to learn the size of San Francisco’s budget, and said it likely speaks to the politics here of high taxation for robust services.

“The consolidated government argument explains some of the difference, but I don’t think it’s all of the difference,” she said. “Why do places differ? There are things that are easy to measure, like population and demographics. And there are things that are harder to measure, like politics and culture.”

Gordon provided data from 2012 that showed San Francisco ranked No. 3 in revenue per capita compared with 28 other combined cities and counties. Just Washington, D.C., which essentially functions as a state, too, and New York City, with its unusual system of five boroughs, took in more per resident than San Francisco.

Whether San Francisco’s big budget is a good thing or a bad thing depends on who you ask. Supervisor Aaron Peskin, who voted against the budget and opposes the sales tax and City College parcel tax on the November ballot, said he’s concerned about what all this spending will mean when the inevitable economic downturn strikes.

“We’re in the middle of an affordability crisis, and City Hall is continuing to do more with more instead of more with less,” he said. “I can’t walk around the district that I represent without people noting the obvious, which is that their taxes are higher and their streets are filthy.”

Deputy Controller Todd Rydstrom said the big budget is to be expected in a booming economic center that has a population surge of 300,000 during the work day.

He added that San Francisco’s high cost of living means higher costs for personnel. Also, he said, the city has prioritized expensive undertakings like a new homeless department, a new international terminal and control tower at the airport and rebuilding San Francisco General Hospital.

“We provide a lot of things that are important to the public and the policymakers here,” he said. “That’s going to really be local government at work.”

San Franciscans seem somewhat conflicted about whether they’re getting enough bang for their many bucks. Most seem to appreciate the extra attention in recent years to parks, playgrounds and libraries, but can’t understand how we spend more than $250 million a year on homeless services and supportive housing and still have some sidewalks that look like Calcutta.

“I don’t have a fundamental problem with the amount of money we spend — if it actually took care of people and built housing and did not let people continue to live and die on the street,” said Mark Hetts, who lives near Buena Vista Park. “It’s a disgrace.”

Joe Maly, a Cow Hollow resident, said he wonders where all the money goes, considering public schoolteachers are underpaid, the roads are in poor condition and the city doesn’t pay for street tree maintenance. In fact, there are only enough arborists on the city payroll to service each of the city’s 177,000 trees once every 105 years. A large tree branch fell on a woman in Washington Square Park just last weekend, critically injuring her.

“For a modern city that’s awash in budget dollars, those things shouldn’t happen,” Maly said.

By the way, we told you recently that San Francisco’s $9.6 billion budget is bigger than the budgets of 13 states. Well, it’s bigger than a lot of countries, too.

According to the Central Intelligence Agency’s World Factbook, San Francisco will take in more money this year than more than 100 countries. In terms of annual revenue, we’re about on par with Sri Lanka and the Dominican Republic.

Among those that will take in less than $9.6 billion in revenue are Aruba, the Bahamas, Barbados and Saint Kitts. Again, editors, I am available for further research.

Heather Knight is a San Francisco Chronicle staff writer who covers City Hall politics. Email: hknight@sfchronicle.com Twitter: @hknightsf