49 per cent use under 100MB but pay for five times the amount.
Mobile price comparison site billmonitor.com says consumers overestimate their mobile data needs to prevent 'bill shock' – excessive charges that come when users run over their limit – though just eight per cent have experienced this.
Almost half of all smartphone users use just 100MB per month or less, though 88 per cent pay for 500MB.
Smartphone data use has risen from 71MB to 154MB per month in the past 18 months, though 27 per cent are 'power users' with over 250MB of monthly data use.
Stelios Koundouros, founder of billmonitor.com, said: "Virtually all smartphone users have one thing in common: they’re all paying more for mobile data than they should.
"It is notoriously difficult for people to estimate their real data usage, and smartphone users who don’t know how much data they are using cannot make an informed decision on which tariff is right for them. We urge people to take a good look at their consumption and make sure that they are not paying over the odds for their data."