TAMPA, Fla. -- Mitt Romney accepted the Republican nomination for president Thursday night with a pledge to create 12 million jobs and to work for American families weakened by four years of economic distress.

"President Obama promised to begin to slow the rise of the oceans and heal the planet," Romney said. "My promise is to help you and your family."

Calling on voters "to put the disappointment of the last four years behind us," Romney, the former Massachusetts governor, also pledged lower taxes, energy independence and a repeal of Obamacare.

In an effort to close a gender gap that has been dragging down his poll numbers, he stressed his commitment to making women equal partners in reviving America.

"When my mom ran for the Senate, my dad was there for her every step of the way," he said. "I can still hear her saying in her beautiful voice, 'Why should women have any less say than men about the great decisions facing our nation?' "

He argued that better economic times are "what Americans deserved" but what Obama has failed to deliver. Four more years of the Obama administration, Romney said, would make things far worse.

The speech was more prose than poetry, failing to rouse the crowd the way his running mate, Paul Ryan had on Wednesday night. Even so, the enthusiastic delegates frequently interrupted Romney with chants of "USA! USA!"

"To the majority of Americans who now believe that the future will not be better than the past, I can guarantee you this: If Barack Obama is re-elected you will be right," Romney told the crowd.

Promising to begin his presidency with "a jobs tour," Romney said he was "running for president to help create a better future. A future where everyone who wants a job can find one. Where no senior fears for the security of their retirement."

Describing himself as a "classic baby boomer," born in Middle America, Romney spent a portion of his address providing a fuller picture of himself, beyond the image of a successful businessman that has become a standard part of his campaign trail stump speech.

Romney talked about providing unconditional love to his five boys but said he always believed his wife had the harder job of raising them while he took endless business trips.

"And I knew without question that her job as a mom was a lot more important than mine. And as America saw Tuesday night, Ann would have succeeded at anything she wanted to."

Much of Romney's story was told throughout the evening by onstage testimonials from people he worked with as the head of Bain Capital and from a lineup of Olympian medalists who praised him for rescuing the 2002 Winter Olympics in Salt Lake City.

A biographical video included a description of Romney as a cheapskate, a man who would replace a stove-hood light with a standard lightbulb.

The portrait was intended to show the fiscally responsible side of Romney, who as governor of Massachusetts cut spending and balanced the state's budget.

The anecdote reinforced the underlying theme of his speech and the convention -- to restore a greatness to America that Republicans believe has been lost by Obama and will be harder to retrieve if he is re-elected.

"You know there's something wrong with the kind of job he's done as president when the best feeling you had was the day you voted for him," Romney said.

He said America yearns for a better future. "It is waiting for us. Our children deserve it, our nation depends upon it, the peace and freedom of the world require it."