Researchers quizzed men and women in the UK on their calorie intake and found the majority of us underestimate exactly how calorific our favourite foods are.
In fact, the study by Laughing Cow showed the average adult estimates there are just 270 calories in a large portion of cinema popcorn, when in fact there can be up to 965.
Brits were also way off the mark when asked to guess the calorie content of a bowl of granola the average adult guessing that a 100g bowl contained 145 calories, but the reality is closer to 450.
A supermarket pepperoni pizza, a staple of many UK freezers contains a staggering 1,100 calories, but respondents guessed an average of 355.
And a large portion of fries is likely to contain as many as 445 calories, however Brits thought it was just 270 - while a double stacked burger has around 500 calories, but the respondents guessed 380.
The study into the nation's eating habits revealed that while the average Brit tries to consume 1,920 calories a day, due to the number of snacks consumed throughout the day, the true intake is around 2,635, on average.
More worryingly, over a third of respondents (36 percent) weren't even sure what a calorie is, with two thirds saying they often completely lose track of the number of calories that they consume each day.
Alexandra Labaisse, Brand Manager at The Laughing Cow comments: "Too often we are reaching for snacks that, when we think about it properly, we don't want. Whether it is a soggy sandwich left over after a meeting or a bowl of salty crisps that you devour on auto-pilot in front of the TV, it is clear we will simply graze without much thought.
"However, being mindful about what we are consuming and ensuring we dedicate the time to snack well means we can avoid 'Snaccidents' and enjoy a delicious snack without the guilt. The Laughing Cow is the perfect portion-controlled snack, starting from just 25 calories per triangle."
The average adult thought a typical 50g portion of prawn crackers contained just 150 calories, when in fact it is nearer to 285.
Many Brits are also clueless when it comes how many calories men and women need to maintain their weight, with as many as 12 percent thinking men need as many as 3,000 calories to stay the same weight, when actually it is 2,500.
Almost two in ten women (18 percent) had no idea what a typical woman needed to consume to maintain their weight.
The poll of 2,000 Brits also found that 17 percent of adults exceed their calorie allowance every day of the week, with the average adult in the UK checking the calorie content on packaging just four times a week.
A quarter of adults said if they knew how many calories their favourite snacks and treats contained, it would stop them from eating them.
Six in ten adults said they were amazed when they learnt how many calories were in their beloved foods and soft drinks. Wine, lager and cola were among the only foods where adults over estimated the calorie content.
1. Slice of chocolate cake (70g) - actual calorie content: 310; Brits think the calories are: 255
2. Milk chocolate bar (45g) - actual calorie content: 240; Brits think the calories are: 200
3. Bowl of granola (100g) - actual calorie content: 450; Brits think the calories are: 145
4. Prawn crackers (50g) - actual calorie content: 285; Brits think the calories are: 150
5. Peanut butter (2 tablespoons) - actual calorie content: 365; Brits think the calories are: 155
6. 1 poppadum - actual calorie content: 125; Brits think the calories are: 100
7. Large Cinema Sweet Popcorn (198g) - actual calorie content: 965; Brits think the calories are: 270
8. 1 supermarket pepperoni pizza (490g) - actual calorie content: 1,100; Brits think the calories are: 355
9. Large fries - actual calorie content: 445; Brits think the calories are: 270
10. Double stacked burger - actual calorie content: 500; Brits think the calories are: 380