The cut to Scottish benefits will be nearly twice as high as UK government estimates and could result in 17,000 job cuts, according to the deputy first minster.
The UK government estimated that its welfare reform programme will save £2.5 billion in Scotland by 2015, but new analysis by the Scottish government puts the cut at £4.5 billion, Nicola Sturgeon told delegates at the SNP Conference on Sunday.
The analysis states that 2014/15 welfare bill is expected to reduce by £21 billion across the UK, and by around £2 billion in Scotland as a result of the UK reforms since 2010.
But the Scottish government paper also assesses the "cumulative impact" of all of the cuts in the UK Budget, autumn statement and spending review, and comes to a total of £4.5 billion.
Nearly a quarter of the cuts will directly impact on children, Sturgeon told SNP delegates.
"The Tories estimate that their welfare cuts will amount to £2.5 billion in Scotland by 2015," she said.
"I asked Scottish government officials to check the figures and I am publishing that analysis today.
"And guess what? It seems the cumulative cut by 2015 will not be £2.5 billion. It will be £4.5 billion.
"£4.5 billion taken from the purses and wallets of ordinary, hard-working people right across Scotland who can least afford it.
"It's an utter disgrace. And make no mistake, it will be hard-working people that will feel the pain, and disabled people too.
"Not the so-called scroungers and skivers portrayed by the smug Osborne.
"The clue is in the names of the benefits being cut - working tax credit, disability living allowance, child benefit.
"And, of course, money out of people's pockets is money out of the economy. Welfare cuts of this magnitude will cost the Scottish economy 17,000 jobs.
"But do you know the most shameful thing of all? £1 billion of these cuts are benefits that directly support children.
"That's equivalent to a cut of more than £1,000 for every child in Scotland under the age of 16.
"So there you have it, the awful price of letting Westminster control our resources and take our decisions for us."
Sturgeon also revealed she cried when she signed the Referendum Bill that will pave the way for the poll on September 18 2014.
"When I joined this party at 16 years of age I never imagined that I would put my signature on a Scottish Independence Referendum Bill," she said.
"But that is exactly the privilege I had last Wednesday.
"I don't mind telling you, I had a tear in my eye as I did it.
"I thought of all those men and women down the generations whose efforts and sacrifices have helped bring us to this moment in our history."
Sturgeon added: "We simply can't afford to pass up this precious opportunity to set our country on the right track.
"The truth is there is no country in Europe that should be more confident about its economic future than an independent Scotland.
"We have vast potential for renewable energy. We have a multibillion-pound food and drink sector, thriving life sciences industry.
"We are world class at attracting investment from overseas. We have some of the best universities in the world.
"We have produced some of the greatest entrepreneurs the earth has ever known.
"And yes we have oil and gas in abundance. And I'll let you into a wee secret - having oil and gas reserves worth £1.5 trillion is not really a problem.
"It's not the sum total of our economy, but it's a massive advantage that other countries would give their eye teeth for.
"And it's high time Scotland started getting the benefit of it."
Scotland's relative wealth should be the centrepiece of the SNP's independence campaign over the next 18 months, the Deputy First Minister suggested.
The pro-UK Better Together campaign has warned an independent Scotland would be over-reliant on oil, a volatile resource that has contributed up to 20% of Scotland's income in the past.
But Sturgeon said Scotland has consistently contributed more to the UK over the past 30 years, regardless of how low the oil receipts have dipped.
"For every one of the last 30 years we have generated more tax revenue per head than the UK as a whole," she said.
"If there is one fact I want you to remember over the next 18 months and tell everyone you know, it is this one.
"During those 30 years, oil prices will have gone up and they will have come down.
"The economy will have grown and it will have been in recession.
"But one fact has remained constant. In every single one of those 30 years tax receipts per head of population in Scotland have been greater than tax receipts per head of population in the UK."
Responding to Sturgeon's claim that Scotland was facing £4.5 billion of welfare cuts, a Scotland Office spokesman said: "These figures from the Scottish government are unofficial, crude and misleading and should be subject to a good deal of scepticism.
"It also shows they cannot tell the difference between benefits and the payments made to families and children.
"The fact is that the UK spends around £20 billion on welfare and benefits in Scotland every year and the Scottish government has yet to explain how it would sustain that level of funding if Scotland leaves the UK for good.
"The population share method they apply to benefit expenditure is also crude. Their own table shows that, using their method, Scotland is protected relative to its population share in over half of expenditure, including housing benefit and the state pension as part of the UK.
"Given the evidence of the recent leaked document which showed the stark difference between the Scottish government's thinking in public and private, people in Scotland would be forgiven for treating this figure with some suspicion."