But virtually no-one uses that much because, as Auckland GP Dr Steve Taylor notes, "you end up like a grease monkey".
Beiersdorf, the supplier of the Nivea range of sunscreens, recently received a "small number" of complaints from sunburnt customers - some of which involved a recently reformulated product, Nivea Protect and Moisture Sunscreen Lotion.
In response the company said: "Complaints regarding ineffective sunscreens can often be the result of inaccurate application.
"We know that most people do not apply a sufficient amount of sunscreen."
Nivea was following up quickly with customers, "to establish any possible reasons for issues with product performance", but also said the new formula had been rigorously tested against the Australia-New Zealand standard for sunscreens.
Nivea recommends one teaspoonful of sunscreen for each of the seven areas of the body: each leg, each arm, the front of the torso, the back and the face and neck.
The dermnetnz.org website, run by skin specialists, recommends applying a second "coat" of sunscreen 30 minutes after the first and thereafter every two hours, or more often if it is likely to be washed or rubbed off.
Sunscreens' known limitations mean they shouldn't be fully relied on, which is why manufacturers and health agencies recommend additional measures such as seeking shade, wearing a long-sleeved shirt and long pants or a long skirt and a broad-brimmed hat.
The Cancer Society also recommends to pick a product that is "broad spectrum", to filter out ultraviolet A and B solar radiation.
Dermnet says: "Always choose a sunscreen which has at least one of its ingredients that protects across the full UV-A range. These include the metal oxides, titanium dioxide and zinc oxide, and the chemical absorbers, avobenzone, ecamsule, bemotrizinol and bisoctrizole.
"The UV-A protection factor (UVA-PF) must be at least one-third of the labelled SPF so choosing a sunscreen with a higher SPF will also mean a higher UV-A protection."
