Oasisdress2I've had my eye on this Oasis dress for ages, and was happy to see it in the sale last night (£30 - and  it's much nicer and sexier in real life). Sadly, they had every size except mine, and no amount of squeezing into the size smaller or 'allowing for room' in a size bigger got me the fit I wanted. So while I cursed the Islington branch and planed ways of skiving off work early to try central London this afternoon, I got thinking about sizing on the UK high street. I quickly realised that I don't really have a clue what dress size I am. I can go into one shop and easily fit into a size 12, yet I have dresses from H&M in a size 16. Why is it that a medium drowns me in one place, while a large clings in all the wrong places elsewhere? What dress size am I? Well, that depends on the shop...

To help you on your travels, I've come up with CQ's guide to High Street sizing. This isn't foolproof, but hopefully it'll help you to take the right size into the fitting rooms!

Topshop: Runs true-to-size with a leaning towards small. Dresses, tops and skirts are - as a rule - more generous than trousers. Jeans run small around the thigh area.

Miss Selfridge: Similar to Topshop, though can run slightly smaller in some cases. Jersey tops are generally quite generous, though this is not a shop for those with big boobs!

H&M: Generally runs very small with the odd item (often tees and vest tops) cut ridiculously big. Blouses and button-down dresses are small across the back, but smock-style items run big. Size labels are European, though at H&M, a size 16 is a 42, while that's a 14 from other European brands.

Dorothy Perkins: Almost always runs big (so great on fat days). Generously cut around the waist. Does different leg lengths for trousers, which is very useful.

New Look: Generously sized. Trousers often run very big around the hips and waist. Shoes are also quite well-sized (great if you're a half size). If in doubt, go a dress size smaller than you would in Topshop or H&M. Lingerie runs slightly smaller so beware of buying tiny knickers!

Warehouse: As a rule, quite reliably true to size, though trousers can be a bit slim-fitting. Jersey dresses hide a multitude of sins and are usually very well cut for the price.

Oasis: Runs quite big, but varies from style to style so try things on before buying. Cotton items tend to be roomy, and the top-half is always well-cut for more voluptous ladies, but fitted styles (dresses in particular) can be small around the hips in particular.

Gap: Jeans (especially the hipster styles) have a tendency to run big and stretch VERY quickly, so take the shop assistant's advice and go for the smaller size to allow for some give. Tops run small, so be careful - especially with items marked S, M, L (10, 12, 14 ish). American sizing on Gap labels converts to UK equivalent by adding 4 (thus a Gap 4 is a UK 8, a 6 is a 10 and so on).

Primark: Try things on! As you'd expect from a cheap shop, sizing is very unreliable, but as a rule things run surprisingly big. Skinny jeans stretch quickly, so go a size smaller. Most tees are in combined sizing; 8 - 10, 12 - 14 etc. Dresses are generally quite roomy but beware if you're more than a C-cup that they may be tight around the bust.

River Island: A tendency towards cutting small, though you can often find trousers and jeans that are strangely large. Another place to definitely try before you buy!

Jane Norman & Morgan: Both cut very small and stop (with many styles) at a size 14. One best left to the young and slim!

Marks & Spencer: Generally runs slightly large. T-shirts are generous so go a size smaller for a closer fit. Waists on trousers and skirts tend to be cut slightly higher than the younger trend shops, so your usual size will probably drop to the hips a little. Shoes come in half sizes, which is great news. Lingerie is reliably well-sized.

Next: Similar to Marks & Spencer, things are generally quite well-cut and true to size or slightly large.

Mango & Zara: Runs very small (European sizing again) but great if you're tall as trousers and jeans tend to be very long in the leg. Flimsy cotton items in particular are very tiny, so try things on and don't worry too much if you need a larger size.

Peacocks: Similar to Primark - sizes vary, but generally they're true to size or large (vests are very big so watch out).

Debenhams: Designers at Debenhams is notoriously generous - especially the logo t-shirts and floaty items. Bikinis are also surprisingly generous, so take advantage of fitting into a smaller size!

Matalan: Some items - vests, jeans, blouses run big, but for some reason dresses are very slim-fitting, especially if you have a broad back. Try things on before buying!

Wallis: Similar to Dorothy Perkins, cut generously so you can often fit into a size smaller than usual, but try on before buying.

Monsoon: Generally true to size or slightly generous, with sizes going higher than most high street shops. I would say something about the trouser length, but do you know anyone who goes to Monsoon for trousers?!

Disagree? Remember these guidelines are based on the experiences of myself and the other Shiny girls, and chances are you don't have the exact same body shape as us! Share your experiences below if you've got more to add, we'd love to hear your thoughts.