The revised estimate, from the Scottish Trades Union Congress (STUC), follows the publication of a report by the Office for National Statistics (ONS) on the scale of use of these type of contracts - which don't guarantee minimum hours - across the UK.
The union body said there are least 118,720 zero-hours contract jobs north of the Border, with the number of people being hired on such contracts doubling over the past decade.
Stephen Boyd, STUC assistant secretary, said the ONS figures had for the first time included data from employer as well as employee surveys. He said: "This is basically a better measure, as the number has been underestimated in the past."
And he added: "Previous estimates were derived from employee surveys, but many people did not know they were on zero-hours contracts. The new figure reflects that people now have better awareness of the nature of their employment contract, so they are more likely to report it accurately
"They have also used employer surveys this time as well, and obviously companies know exactly what kind of contracts people are on.
"It is really quite stunning the number of people that are on these contracts."
The use of zero-hours contracts has come under increasing scrutiny for tying workers into insecure and low-paid employment. But the true scale has been difficult to pinpoint, with a lack of official figures.
Estimates by the ONS in 2012 put the number of zero-hours contract workers in the UK at around 200,000. That figure was revised to 583,000 at the end of 2013.
But the fresh ONS snapshot published at the end of last month, which included the survey of employers for the first time, showed 1.4 million jobs across the UK were offered on such a basis.
Boyd said the estimates could not be read as showing a huge leap in zero-hours contracts over the last couple of years.
But he added: "We do know there has been very significant growth and it would be a reasonable assumption the numbers have doubled over the last decade.
"In Scotland, that probably implies about 50,000 more people on zero hours than a decade ago, so it is a huge issue."
Last week, the UK government said jobseekers will risk losing benefits if they turn down certain zero-hours contracts without "good reason" under the new universal credit system.
Claimants could face sanctions and lose payments for more than three months if they refuse to take up such jobs.
Boyd said: "People might be poor on benefits, but there is a degree of security there as they know what they are getting. If you move onto a zero-hours contract, you are going to be poor and in work, but not know what you are going to be working from one week to the next."
An interim report published last month on an inquiry by the House of Commons Scottish Affairs Committee into zero-hours contracts concluded that "too often, the relationship is unbalanced, leaving the employer with all of the flexibility and few costs and the worker in fear of dismissal, denied access to due rights of employment and, in some cases, earning less than the minimum wage".
Employment law is reserved to Westminster. In December, UK Business Secretary Vince Cable ruled out banning zero-hours contracts, but announced a consultation on the issue looking at areas such as exclusivity, where some workers on zero-hours contracts are not permitted to take on other employment.
A spokeswoman for the Department for Business, Innovation and Skills said the result of the consultation, which closed in March and received around 36,000 responses, would be published "in due course".
Alexander Ehmann, deputy director of policy at business organisation the Institute of Directors, said for workers such as consultants, students and those nearing retirement, a zero-hours contract makes "perfect sense".
He said: "Some businesses need employees on a flexible basis to allow them to deal with peaks and troughs in demand, retain trained people for occasional work, or try out new business projects."
But he added: "Contracts which do not allow people to look for additional work may be justified in some cases, but they also create the chance of unfair treatment, so the government should seek to curb their use."
The Scottish Government has also urged Cable to address the issue of exclusivity clauses, in a letter from Enterprise Minister Fergus Ewing in response to the consultation.
He also highlighted research which found that 40% of those on zero-hours contracts said they had shifts cancelled without notice.
Ewing said: "[We] would urge the UK government to look at ways in which compensation can be paid or a minimum income secured where shifts are cancelled."