A 1MB limit is one of the strictest requirements you will encounter on any submission portal, and it requires a different approach than simply running a file through a compressor. Getting to 1MB requires understanding exactly what is causing the size and removing or reducing that specific thing, not just applying generic compression and hoping for the best.
For PDF files
The most important first step for any PDF under a strict size limit is to count the pages and ask whether every page is genuinely required. A three-page document under 1MB is achievable for almost any content type. A seven-page document under 1MB requires aggressive compression that may affect readability.
For scanned PDFs, grayscale conversion combined with moderate compression is the most effective approach. A single scanned page in grayscale at 150 DPI is typically between 50KB and 150KB depending on content complexity. Three pages should comfortably fit within 1MB. If you have more pages than will fit at reasonable quality, splitting and uploading as separate files is preferable to compressing so aggressively that the document becomes unreadable.
For digital PDFs, the text itself contributes almost nothing to file size. The size comes from embedded images. Remove the images, replace them with compressed versions, or delete pages that contain large images if they are not essential to the submission.
A one-page typed letter or certificate exported cleanly from a word processor as PDF should be under 50KB without any additional compression. If yours is above 500KB, re-export from the source application using a screen quality or compressed PDF setting rather than a print quality setting.
For images
Getting a photograph under 1MB is straightforward at any reasonable size. A 1200 by 800 pixel JPEG at 80 percent quality is typically between 100KB and 300KB. The challenge is when the image needs to maintain enough detail for a specific purpose.
For images that will be viewed at full size by a reviewer, 1200 pixels wide is the minimum that looks credible. At this size and 80 percent JPEG quality, most photographs will be well under 1MB. If the image is above 1MB at 1200 pixels wide, try reducing to 1000 pixels wide or reducing quality to 70 percent and checking whether the result remains acceptable.
For screenshots and diagrams that must remain sharp, use PNG at 1000 pixels wide. A clear screenshot at this size should be between 100KB and 400KB depending on content complexity. If you must use JPEG for a screenshot for size reasons, use quality 90 percent or above to minimise text blurring.
For Word and Office documents
A text-only Word document should be well under 1MB at any reasonable length. If yours is not, the cause is almost certainly embedded images or revision history.
Remove all images from the document, compress them separately using image tools, and re-insert the compressed versions. Alternatively, export the document as a PDF, which strips all Office-specific overhead and produces a file that reflects only the actual content.
For presentations, 1MB is an extremely tight limit. Remove all embedded photos and replace with compressed versions. Remove all embedded videos. If the presentation still exceeds 1MB after all images are compressed, splitting into multiple files and presenting them sequentially is the only option that preserves content quality.
When to use splitting instead of compression
Below about 200KB per page, text in scanned documents becomes difficult to read for many viewers. If getting a multi-page document under 1MB would require compressing to this level, splitting is a better choice than compromising readability.
Check whether the portal requiring the 1MB limit has multiple upload fields or accepts multiple file attachments. Many portals that seem to have a single strict limit actually have separate fields for each document type, each with its own 1MB limit. Uploading your transcript, certificate, and motivation letter to three separate fields means each has its own 1MB budget rather than all sharing a single budget.
Checking file size accurately
File size as shown in your application and file size as the portal measures it can differ slightly due to how different systems count bytes versus kilobytes versus megabytes. Some systems define 1MB as 1000KB, others as 1024KB. The difference is small but matters at the boundary. Target 950KB rather than exactly 1000KB to give yourself a safe margin.