When Sarah* gave $150 as a gift for her friend's wedding, she says she "didn't really give it a lot of thought".

It seemed like a reasonable amount, and she'd already chipped in some money coordinating the hens party and organising bridal events.

But after the wedding, her friend confided that she'd been disappointed by the amount of money she and her new husband had received in their "wishing well", a donation box for guests to give cash to the newlyweds.

"She had expected the wishing well funds would cover the costs of the wedding — or at least come close to it," Sarah says.

"Once I realised that a friend had given $50 more than me, that's when I really started to spiral and thought, 'Oh God, I've made a huge mistake'."

Sarah shared her experience for ABC RN Life Matters' Too Hard Basket, asking RN listeners if she was living in a "pre-inflation wedding-guest world".

Her query garnered more than 700 social media responses.

"It sounds like your friend has developed a contemporary affliction: Gratitude Deficit Syndrome," wrote one commenter.

"I thought weddings were a celebration, not a money-making enterprise," wrote another.

But although the vast majority of commenters said Sarah's $150 contribution was generous, she can't shake the feeling that she's made a critical faux pas.

"I feel like an absolute cheapskate, and there's nothing I can do about it now," she says.

Why does wedding gift etiquette elicit such strong feelings? And is there a "magic number" to help make the decision easier?

Irish whiskey and hard haggling

Wedding gifts have a rich history, from dowries in ancient Mesopotamia to the earliest gift registries by department stores in the 1920s.

Many would remember glory boxes or hope chests, filled with domestic items and gifted to new brides in the 40s and 50s.

Now, as more couples live together before marriage, cash is the gift du jour — although in many cultures, this is a long-held tradition.

Wedding gifts have long signified more than well-wishes for a bride and groom, says Kiera Lindsey, a research fellow at Griffith University and history advocate at The History Trust of South Australia.

"In the Irish tradition, families were known to sit down at the haggling table for two to three days and with 10 bottles of whiskey before they finally got to the bottom of what they agreed," she says.

If bridal gifts couldn't be agreed on, there could be "an almighty skirmish that could rent a community or inter-country or inter-clan alliance asunder".

Historically, throughout many cultures, Dr Lindsey says weddings have been largely about social mobility, which has been reflected in the gifts bestowed upon a married couple.

"The question is: what does the community give in return for what it receives from the celebration of this new union, hopefully a union that is going to make a contribution back to society?" Dr Lindsey explains.

And for those with money to burn, wedding presents are an excellent opportunity to show off one's wealth and status.

Take, for example, the lavish 20,000-seat stadium gifted by the ruler of Abu Dhabi to his son; the world's most expensive perfumes, adorned with gold and diamonds, given to Prince William and Kate Middleton by a famous parfumier; and the Greek island given to sports agent Jorge Mendes by footballer Cristiano Ronaldo.

Finding the magic number

For those with more limited means, deciding how much to spend on a wedding gift — particularly if the couple has opted for cash — often comes down to a gut feeling.

In many cultures, that also means taking into account auspicious numbers, familial ties and the opinion of a patriarch or matriarch.