As a photographer you should be shooting RAW, the ONLY exception would be if your employer requires you to shoot jpg. … but IMO you should convince them they are wrong.. you are potentially missing a lot of details, and may not be able to save an otherwise decent picture. Shooting RAW captures more information and allows for potential of higher quality images, just do it, get used to it and reap the benefits. That said, you will need to convert the RAW file at some point for printing, or sharing to your website or social media.

What size do I need?

Print

Last week I mentioned you need 240-300dpi for high quality printing, refer to your printer manual, or contact your professional print service for required specifications.

So depending on your print size you should scale the image appropriately. dpi = dots per inch, 300 dpi = 300 dots per inch.
Therefore an 8″X10″=8(300)X10(300)= 2400px X 3000px, to properly print an 8X10 at 300dpi you need the minimum resolution of 2400px X 3000px.
If the printer requires 240dpi then an 8″X10″ = 8(240) X 10(240) = 1920px X 2400px.

The formula is simple— Width(DPI) X Height(DPI) = your minimum image size.

Ok… But how do I re-size them?

My preferred method is Lightroom. Once you’ve made your edits and cropped the image select Export.
In File Settings select image format JPEG, quality 100, colour space sRGB
Under Image Sizing set Resolution to 300 ppi

This fill give you the largest jpg file – this is your High Resolution File. – Send this to your printer, or downsize to required size.

Blog

For blogging you do not need the same resolution, nor would you want to post it.
Sidebar- Your goal as photographer is to sell your client beautiful images to display on their walls. To assure they get the quality work you must take control of the product from capture to print. If you post a full size image at high resolution, not only will it take forever to load, but you encourage people to print direct from your site. They could then print from home or take it to ‘Discount Dan’s Photo Hut’ and print direct from file. It may work out for them, but odds are the image will not be colour corrected properly, and the client will think you took a bad picture. You also miss out on sales you need to recoup the time you have invested in those images.
So back on topic..

Web standard is 72 dpi, it would require an entire post or two to explain this, but basically images on the web are determined by their pixel size more than dpi.
For your blog post a watermarked image of 1500 pixels wide. It provides a nice representation for a client to decide if that is the image they wish to print.
Out of habit I save these images at 90dpi.. current 27″ imac is at 109dpi, but again, it really won’t make much difference.
File Settings- JPEG Quality 80-100 sRGB
Image settings- resize to fit long edge 1500 pixels Resolution 90 ppi
Watermark

Facebook

Facebook automatically resizes and formats your images when you add them. But to help make sure your images display in the highest possible quality, the following is suggested by Facebook.

Resize your photo to one of the following supported sizes:
Regular photos: 720px, 960px, 2048px (width)
If you use a 2048px photo, make sure to select the High Quality option when you upload it
Cover photos: 851px by 315px
To avoid compression when you upload your cover photo, make sure the file size is less than 100KB

As above save your image as a JPEG with an sRGB color profile.

an alternative to resizing in Lightroom is use Photoshop, selecting Image->Image Size, then either a preset from drop down, or create a custom.

Then save as JPEG

That should help a bit more with sizing and printing, keep sending questions and I’ll answer if I can.