How to scan documents with your phone so the PDF stays small and still readable

Your phone captures each page at far more resolution than text needs, which is why three scanned sheets can top 5 MB. Here's which filter to pick, how to scan on iPhone and Android, and what to do when the PDF already exists and doesn't fit.

By Robert Bzia·Updated October 28, 2026·7 min read

Your phone has become the household scanner. The trouble starts when you upload the result: the form wants the contract, the payslip and your ID in 2 MB at most, and the four pages you've just scanned weigh 9 MB. You haven't done anything wrong; the camera simply captures far more information than a sheet of text needs.

In this guide we explain where that size comes from, which setting cuts it the most without it showing, how to scan step by step on iPhone and Android, and what to do when the PDF already exists and doesn't fit. The steps for Notes, Files and Google Drive and the retirement of Microsoft Lens were checked in October 2026 against the official documentation from Apple, Google and Microsoft, which we cite at the end.

Why a document scanned with your phone is so large

A mid-range phone camera takes 12-megapixel photos (4032 × 3024 pixels). If an A4 page fills the frame, those pixels are like scanning it at about 345 DPI, more than twice what you need: 150 DPI is enough for text to look sharp on screen and on paper, as we explain in the guide on why a PDF is so large. And if the page is saved in color, each dot takes three times as much as in grayscale.

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The final file takes far less than those figures, because the images are compressed as JPEG, but the proportion holds: the color photo has about 17 times more data than the page at 150 DPI in grayscale, and to the naked eye the text reads the same in both. Scanning apps crop and straighten the page, but the resolution they save it at is up to each app and can hardly ever be chosen. What you do control is color, light and framing.

The setting that changes the size most: the filter

The scanner in Notes and Files on iPhone offers four filters: Color, Grayscale, Black & White and Photo. Google Drive also lets you change the filter of each page after capturing it. Choosing well is the most effective thing you can do: before compression, a page in grayscale has a third of the data it has in color. After compression the real saving is smaller, but it's usually noticeable, and a text document reads exactly the same.

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Be careful with black and white: it turns every dot into pure black or white based on a threshold. With crisp printed text it gives a clean, light result, but a blue ballpoint signature, a stamp or a faded receipt can come out half-missing or vanish. If you use it, zoom in on the result before saving.

How to scan on iPhone or iPad with Notes or Files

Both apps use the same scanner. These are the steps in Notes, according to Apple's help:

1. Open Notes and create a new note or open an existing one.
2. Tap the attachment button and choose Scan Documents.
3. Before capturing, tap the filters button and choose Grayscale. Depending on your iOS version, the button is at the top or in the bottom bar.
4. Place the page in the frame. In automatic mode it captures by itself; otherwise, tap the shutter or press a volume button.
5. Adjust the corners if needed, add the other pages and tap Save when you're done.

The scan stays inside the note; to send it as a PDF, open it and use Share. If you want a file straight away, use the Files app: go to the folder where you want to save it, tap the More button (the three dots) and choose Scan Documents. When you save, the PDF appears in that folder. To see how much it weighs, touch and hold the file and choose Get Info.

How to scan on Android with Google Drive

Android doesn't have a system-wide scanner of its own, but the Google Drive app, which comes installed on most phones, does. According to Google's help:

1. Open Google Drive and tap the camera button at the bottom right (in some versions, + and then Scan).
2. Point at the page until the outline detects it and take the photo.
3. Crop, rotate or clean up the page if needed, and change the filter to a gray or black-and-white one if the document is text.
4. Add the rest of the pages with the + button.
5. Tap Done, name the file, choose PDF as the format and the folder, and tap Save.

Keep in mind that Drive saves the PDF to your Google account, in the cloud. If it's a sensitive document and you only need it on your phone, download it afterwards and delete it from Drive. Some manufacturers build a scanner into the camera itself: on Samsung Galaxy phones, for example, you have to turn on document detection in the camera settings, and depending on the model it saves an image to the gallery instead of a PDF.

If you used Microsoft Lens, it no longer works: Microsoft pulled it from the app stores in February 2026 and since March 9, 2026 it hasn't created new scans. It recommends the scanner in the OneDrive app instead, which saves scans to the cloud rather than to your phone. And if you pick another app from the store, check whether it processes the document on the phone or uploads it to its servers; in this guide we explain how to check.

Five habits that make a scan smaller and easier to read

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• Scan, don't photograph. Scanning mode crops the page, corrects the perspective and leaves the table out. A normal photo keeps the whole frame, table included.
• Look for even light with no shadows. Daylight near a window, with no shadow from your hand or the phone. Shadows and the grain of a low-light photo are detail the file has to store, and they add weight. On glossy paper, avoid the flash: it leaves a white glare that hides the text.
• Lay the page flat on a plain, contrasting background. A dark table helps the scanner find the edges. Hold the phone parallel to the paper so it doesn't have to correct the perspective so much.
• Choose grayscale for text. Save color for what really needs it.
• Check the size before sending it. And scan only what's needed: every blank back side is one more page.

If you've already scanned it and the PDF doesn't fit

There's no need to do it again. A compressor with a target size saves each page again at just the resolution needed for the limit you type, and in a scanned document you don't lose selectable text, because its text was already an image. The exception: if the app added a text recognition layer (OCR) so you can search the PDF, that layer is lost when compressing this way.

To know whether the result will read well, divide the limit by the number of pages. With 2 MB for four pages you get about 500 KB per page, plenty for sharp text. With 1 MB for ten pages it's about 100 KB per page: the text is still readable, but it starts to show in photos and stamps. If the form accepts several files, another way out is to split the PDF by size instead of compressing it.

Frequently asked questions

Next step

These pages open the tool with the size already set, on your phone too:

• Compress a PDF to 2 MB, the most common limit on government portals and job sites.
• Compress a PDF to 1 MB, for multi-page scans on stricter forms.
• Compress a PDF to 500 KB, when they ask for a single, very light document.

If the PDF already exists and you want to shrink it with what your phone offers, the guide to compressing a PDF on iPhone, Android, Mac and Windows goes over each system. And to see what takes up space in your scan before touching it, run it through the PDF X-ray.

See all guides · Go to the PDF compressor