How to resize an image online

You can resize an image online in the Photopea editor: under Image, Image Size you type the new width in pixels or in percent and the height is calculated automatically. For email, prepare the image twice as wide as the space you are placing it in, so it stays sharp on Retina displays too. A photo straight from the camera is up to fifteen times larger than an email needs.

Key takeaways

1. Resizing an image changes the number of pixels of the whole image and cuts nothing off. Let the height be calculated, otherwise the image gets distorted.
2. A 5760 × 3840 px stock photo is 3.6 MB as a JPG at 80% quality. Resized to 1240 px, it is 242.9 kB, a fifteenth of the size.
3. For Retina displays, prepare the image at double the width. The file is roughly 3.5 times larger than at single size, and at triple the width it is already 7.3 times larger.
4. DPI plays no role on screen. In an email, only the width and height in pixels matter.
5. Make images smaller, not larger. Enlarging adds no detail, it only blurs the edges.

In short: what you need, which width to choose, how long it takes and what can go wrong

• What you need: the image on your computer and a browser. Photopea works online with nothing to install and no registration.
• Which width to choose: double the space in the email. Prepare a full width image for a 650 px email about 1,240 px wide.
• How long it takes: about two minutes per image.
• What can go wrong: a full size photo from the camera loads slowly for recipients, and an image that is too small looks blurry on Retina displays.

What has changed since publication: This article was first published in March 2021. In October 2026 we rewrote it for the current version of Photopea and added resizing in percent, an explanation of DPI and resampling, the advice to prepare images at double size for Retina displays and our own file size measurements. We originally recommended preparing images at exactly their display size in the email. Today we recommend double. We moved choosing the image format into a separate article, JPG, PNG or GIF?

What it means to resize an image

Resizing an image means recalculating it to a different number of pixels while keeping all of its content. That makes it different from cropping, which removes the edges of an image and leaves the rest unchanged. If you need an image at exact dimensions with a different aspect ratio, follow the article How to crop an image to a specific size.

Three different numbers tend to get mixed up when it comes to images. Only two of them matter in an email.

Resampling is the calculation of new pixels when an image is resized. When making an image smaller, the editor merges several neighbouring pixels into one; when enlarging, it calculates the missing pixels. Photopea offers three resampling methods: Nearest Neighbor, Bilinear and Bicubic Sharper. For photos, keep the default Bilinear. Nearest Neighbor does not calculate transitions between pixels and only suits pixel art; on photos it creates jagged edges.

How to resize an image online in 6 steps

We will demonstrate the process in the Photopea editor on a 5760 × 3840 px stock photo that we need across the full width of a 650 px email. Once the margins are subtracted, the image has 618 px of space, so we prepare the file twice as wide, at 1240 px. Photopea is an online image editor that runs in the browser and works much like Photoshop. The basic version requires no registration and no fee, and it shows ads.

1. Open the Photopea editor at photopea.com, click Start using Photopea and then Open From Computer. The editor language follows your browser language. You can also drag and drop the image into the editor window.

2. Go to Image, Image Size to find out how large the image is. The window shows the width, the height and the number of megapixels. You can also open the window with the Alt + Ctrl + I keyboard shortcut. Our photo is 5760 × 3840 px, which is 22.12 megapixels.

   

3. Type the new width in pixels into the Width field, for example 1240. Keep the chain between width and height locked, and the height is calculated automatically. The height changes to 827 px. If you unlocked the chain and overwrote the height, the image would get stretched or squashed.

   

4. Leave Resample turned on with the Bilinear method and click OK. If you turn Resample off, only the DPI value changes and the number of pixels stays the same.

5. Check the result under View, Pixel to Pixel. The editor normally fits the image to the window, so it does not look smaller on screen after resizing. Pixel to Pixel or the Ctrl + 1 shortcut shows the image so that one of its pixels matches one pixel of the screen.

   

6. Go to File, Export as, JPG, set the quality to 70 to 80%, check the file size and click Save. The Save for web window shows the file size in the bottom left corner. Resized to 1240 × 827 px at 80% quality, our photo is 242.9 kB. The image is saved to the downloads folder on your computer.

   

Insert the finished image into the email from your computer or by using the image URL from your website, as described in the guide Email editor of a simple email campaign. The editor scales it down to fit its space on its own.

Try the Quanda email editor

How to resize an image in percent

If you do not need exact dimensions but, say, just half the size, switch the width unit in the Image Size window from Pixels to Percent and type 50. With the chain locked, the height also changes to 50%. A 5760 × 3840 px photo then becomes 2880 × 1920 px.

Keep in mind that half the width means a quarter of the pixels. An image resized to 50% has only a quarter of the original megapixels.

Tip: You can also change the size only when saving. The Save for web window has its own Width and Height fields, so you can make the image smaller right when you export it and leave the original photo in the editor unchanged.

Why you should not enlarge images

Technically you can enlarge an image, just type a larger width in the Image Size window. But the editor only calculates the new pixels from the surrounding ones and cannot create detail that is not in the photo. A small image looks soft after enlarging and its edges are blurry.

Watch out: The most common cause of a blurry image in an email is a small file that the email editor has to stretch into a wider space. Enlarging it in an image editor does not fix this, because the missing detail cannot be added back. Find a larger original instead, for example on a stock photo site or from the photographer.

How to prepare an image for Retina displays

A Retina display is a high pixel density screen that uses two or three physical pixels for every point of the image. Apple introduced the name in 2010 with the iPhone 4, and today they are found in ordinary phones, MacBooks and many Windows laptops. An image exactly as wide as its space in the email gets stretched across two to three times as many pixels on these screens and looks soft.

According to Microsoft's documentation, most monitors used to have 96 dots per inch, and Windows still treats this value as 100% scaling. According to the same documentation, current displays reach around 300 dots per inch and Windows scales the content up. A phone with 460 ppi therefore needs several times more pixels for the same area than an older monitor.

That is why Litmus recommends preparing email images at roughly double the size and points out that the file size grows along with the dimensions. In October 2026 we measured what this costs in Photopea, using a 5760 × 3840 px photo for a full width email image.

Double the width means four times the pixels and, in our measurement, a 3.5 times larger file. Triple the width has nine times more pixels and a 7.3 times larger file. Yet the difference in sharpness between double and triple is barely visible on a phone, which is why we recommend double for email.

Why not send different images for different displays? On the web you can do that with the srcset attribute and the picture element, but according to Can I email neither Gmail nor Outlook supports them. An email therefore needs a single file that works for every display, and double the width is exactly that. How much space an image has in different email layouts is shown in the table in the article How to crop an image to a specific size.

What else you can use to resize an image

Photopea is not the only option. Programs you already have on your computer can also resize an image in pixels.

• Paint in Windows: resize in pixels or in percent while keeping the aspect ratio.
• Preview in macOS: resize under the Tools menu, also in pixels or in percent.
• Quanda email editor: scales the image down to fit its space in the email on its own, but does not change the file size. So always make a camera photo smaller before inserting it.

Tip: iPhone photos are saved in the HEIC format, which most email clients do not display. If you switch your iPhone to Settings, Camera, Formats, Most Compatible, new photos will be saved as JPG. More about formats is in the article JPG, PNG or GIF? Which image file type to use for email marketing.

Checklist before inserting an image into an email

• The image is about twice as wide as its space in the email.
• The height was calculated automatically, and the image is neither stretched nor squashed.
• I made the image smaller, not larger.
• The photo is saved as JPG at 70 to 80% quality.
• The file is tens to a few hundred kilobytes, not megabytes.
• I have checked the test email on both a computer and a phone.

Final thoughts: resizing an image in two minutes

Resizing an image takes two minutes: type the width in the Image Size window, let the height be calculated and save the image at a sensible quality. For email, prepare it twice as wide as the space you are placing it in, and never insert a photo from the camera at full size.

For working with images across the whole email, take the free online course Email Copywriting and Design That Gets Read. If you are stuck with images or with a whole campaign, book a free consultation or write to us at support@onquanda.com.

Good luck!