I used Photoshop but have started to recreate same logo in Illustrator because that's what I'm use to but for some reason I ended up using PS and against my better judgement it's now finished in PS. It's being saved "for the web", GIF file. I've increased the pixel size double of the original and it's only made it slight bigger. What am I doing wrong? The website is not mine but I made the logo for the company. It's my first logo being used in a website and they are the one placing and editing the website so I don't know if it's something I'm doing or they're doing wrong. Need some advice!
All image sizes on web pages are controlled by the HTML/CSS. You can write markup to change the size of any image easily. Essentially, the image doesn't change. It is scaled to meet whatever dimensions the HTML/CSS tell it to be.
You need to ask those in charge of the web site as to why the image is being resized. It may be to match the existing design.
Thank you for your answers and you're 100% correct, after reading this and going back to my contact and questioning them it was indeed the CSS used, in creating the website they did not correspond with the web designer on size needed for the placement of logo. This helped me know it wasn't something I did wrong.
If you've saved the image correctly for web in a resolution you've had in mind (e.g. 400x100 px) and it appears quite a bit smaller on the webpage itself then there is a very big chance that the logo location has been marked up with CSS. CSS can give a max-width to your image which scales it down.
You're stating that this isn't your website, so I'd advise to get in touch with the creator of the website if it's not showing well.
What you can do to 100% make sure it's not your image messing up, is to place the image anywhere else on the page to see if it's still smaller than you intended. If that's the case you might have to re-export the image.
Normally a CSS adjustment like this isn't a very big one.
Good luck! :)