How many bytes is a 300 KB file limit?

Two readings are in circulation. Binary 300 KB is 307,200 bytes (300 × 1024); some systems mean 300,000 exactly. This engine targets the binary reading and keeps a safety margin under it, which fits 307,200 comfortably but could sit above a 300,000-byte rule. If your form is unusually strict, use a lower preset and verify the size it reports.

Why did my image come out much smaller than 300 KB?

Because the encoder hit its quality cap before the byte cap. The search never exceeds quality 95%, so a clean, low-detail image that already fits at that setting is returned at that quality — often well under the ceiling. That is the intended behaviour: the tool optimises picture quality inside the limit rather than inflating the file to match it.

Will a 300 KB photo still look good?

For the 1200×900 test photograph the engine kept every pixel and used quality 68%, which is a normal web-delivery setting; the visible change sits in fine texture rather than in edges or colour. Images with more detail than that, or larger dimensions, may need a lower setting or a smaller frame to fit.

Can I compress a PNG to 300 KB and keep it a PNG?

Not with this engine. It encodes JPEG or WebP, because reaching a hard byte ceiling on a lossless format is not something a quality slider can guarantee. Transparent artwork should go out as WebP, which keeps alpha; flat logos often reach 300 KB as WebP without visible loss.

Free & Private Image Compression Preset

Compress Image to 300 KB

Fit an image inside 300 kilobytes — 307,200 bytes — without it leaving your machine. This is the ceiling where the quality search still has room to work: on a busy 1200×900 photograph the engine spent almost the entire budget and returned 296.9 KB at quality 68% with no resizing at all, while a smoother 439.6 KB photo stopped at the encoder's own 95% quality cap and came out far below the limit. Both runs, including the WebP comparison, are measured in Chromium and printed below.

How to use this 300 KB preset

Step 1: Drop the Photo In

JPG, PNG and WebP files are read straight into browser memory through the File API. Nothing is posted to a server, so the step works the same on a phone connection as on an office network.
Step 2: The 300 KB Target Is Already Set

Target File Size mode opens on 300 KB. The engine encodes at quality 95% first; if that overshoots 307,200 bytes it steps quality down toward 30% and keeps the largest file that still fits.
Step 3: Read the Number Before You Submit

The result panel shows the byte size, the output dimensions and the quality that produced them. If a form cares about the limit, confirm the figure on screen rather than trusting the filename.

Preset features & capabilities

It Spends the Budget It Is Given: The search stops at the highest quality that fits under the ceiling minus a small safety margin, so you get the best picture the limit allows instead of a needlessly small file. On the 566.7 KB test photo that produced 303,982 bytes.
Dimensions Usually Stay Put: Pixel reduction only begins when quality 30% still overshoots the target. Neither measured run at this ceiling resized anything: the outputs kept 1200×900 and 1376×768 respectively.
Two Containers, One Ceiling: WebP is available next to JPEG. On the noisy test photo WebP needed quality 59% to reach 303,936 bytes — the same size as a JPEG at quality 68%, which says the image content, not the container, is doing the limiting.

Worked example

Input: Test photograph sample-noisy.jpg from this repository: 1200×900 pixels, 580,334 bytes on disk (566.7 KB) — above the 307,200-byte ceiling, so this one had to give something up.

Output: After compression to a 300 KB target: 303,982 bytes (296.9 KB), dimensions 1200×900 pixels, quality 68%. That lands 3,218 bytes under the 307,200-byte ceiling, a 48% reduction on the original. WebP output for the same file measured 303,936 bytes at quality 59%. Second run: sample-photo.jpg (450,169 bytes, 1376×768) compressed to 162,175 bytes at quality 95%, 1376×768 pixels.

Measured in real Chromium with the same engine this page runs. Quality 68% was the highest setting whose JPEG still fitted under the ceiling, and the 1200×900 frame was never touched. The same file as WebP needed quality 59% to reach 303,936 bytes.

Honest limits & caveats (300 KB)

A heavily textured source — foliage, gravel, crowd scenes, film grain — can be pinned against the cap at a moderate quality setting, while a clean flat graphic finishes far below it because the encoder refuses to pass its own 95% quality ceiling.
An image already smaller than 307,200 bytes is returned unchanged rather than re-encoded, so a file that already fits never takes a second quality hit.
A PNG with real transparency becomes an opaque JPEG if you pick JPEG output, and the transparent area fills with white. Choose WebP when the alpha channel has to survive the pass.
Small print inside a photograph survived this target in our runs, but readable is not the same as guaranteed: open your own output at full zoom before submitting a document image.
The figures here describe two committed sample files run through this exact engine. Your dimensions, colour depth and noise level all move the result, so treat them as a worked example and not a promise.

Tips for best results

Some forms say 300 KB and mean 300,000 bytes rather than 307,200. If yours looks strict, aim a little lower or switch to the 200 KB preset and check the number on screen.
Start from the largest clean source you have. Each extra JPEG generation discards detail permanently, so compressing an already-compressed export costs more than compressing the original once.
For screenshots and graphics built from flat colour, WebP normally lands smaller than JPEG at the same quality number.
Queue several files and each gets its own independent search toward the ceiling; the whole set downloads as one ZIP archive.

Frequently Asked Questions (FAQ)

How many bytes is a 300 KB file limit?: Two readings are in circulation. Binary 300 KB is 307,200 bytes (300 × 1024); some systems mean 300,000 exactly. This engine targets the binary reading and keeps a safety margin under it, which fits 307,200 comfortably but could sit above a 300,000-byte rule. If your form is unusually strict, use a lower preset and verify the size it reports.
Why did my image come out much smaller than 300 KB?: Because the encoder hit its quality cap before the byte cap. The search never exceeds quality 95%, so a clean, low-detail image that already fits at that setting is returned at that quality — often well under the ceiling. That is the intended behaviour: the tool optimises picture quality inside the limit rather than inflating the file to match it.
Will a 300 KB photo still look good?: For the 1200×900 test photograph the engine kept every pixel and used quality 68%, which is a normal web-delivery setting; the visible change sits in fine texture rather than in edges or colour. Images with more detail than that, or larger dimensions, may need a lower setting or a smaller frame to fit.
Can I compress a PNG to 300 KB and keep it a PNG?: Not with this engine. It encodes JPEG or WebP, because reaching a hard byte ceiling on a lossless format is not something a quality slider can guarantee. Transparent artwork should go out as WebP, which keeps alpha; flat logos often reach 300 KB as WebP without visible loss.