How to actually hit the number.

1 · Why a portal cares about kilobytes at all

Government upload fields were built for 2012 bandwidth and 2012 servers. A 6 MB phone photo times 2 million applicants is 12 TB of ingress on a single last date — so the form hard-codes a ceiling. Your “High Quality” export is irrelevant: if the bytes on disk are 367 KB and the cap is 300 KB, the server answers File size exceeds limit before it ever looks at the pixels.

The classic trap is the “Extreme” slider. Tools like iLovePDF and Smallpdf offer Low / Medium / Extreme. Extreme on an 800 KB scan often lands at 367 KB. The portal asked for 300. The fix is not a vague quality level but a search that stops only when the byte count is under the cap — what UnderKB does: binary-search JPEG quality (and, only if needed, pixel dimensions) until the file is actually ≤ the number you typed.

1 KB = 1024 bytes on every portal that validates server-side. “Exactly 20.0 KB” = 20 × 1024 = 20 480 bytes. Filesystems round to KB, validators do not — a file that shows as “20 KB” in your file manager can be 20.4 KB (20 890 bytes) and fail. Target 19 KB when you need a 20 KB ceiling.

2 · The four checks that decide acceptance — in the right order

1. Format first. Most Indian form validators check MIME before size. Photo fields usually accept JPEG only; a PNG renamed to .jpg fails even at 14 KB. Signature fields are the exception: many now accept PNG (transparent) or JPG. Check the notification line that says “JPG/JPEG only” — it is not a suggestion.
2. Dimensions second. “3.5 × 4.5 cm” is a print size. Pixels depend on DPI. At 144 DPI, 3.5 × 4.5 cm ≈ 200 × 230 px (SSC). At 300 DPI, the same print size ≈ 413 × 531 px (passport print). The portal checks pixels, not centimetres — so fix centimetres and pixels with the passport tool before you compress.
3. Range third. SSC photos are 20–50 KB, not “≤ 50 KB”. A 14 KB photo fails SSC just as a 60 KB one does. Use both Maximum and Minimum fields when the notification publishes a band.
4. Background last. Cream walls, shadows and old photos are auto-rejected by colour-ratio checks on several portals. Shoot against a plain white wall in daylight before any compression — no encoder fixes a grey background.

Order matters. Compressing before fixing dimensions produces a sharp file at the wrong pixel box — still rejected, and you have added a generation of JPEG loss.

3 · KB maths you can do on the back of a form

Intuition: a 200 × 230 px SSC photo is 46 000 pixels. At 0.4 bytes/px (JPEG quality ≈ 60) it lands at ~18 KB. At 0.9 bytes/px (quality ≈ 85) it lands at ~42 KB. That is the whole 20–50 KB band in one picture. Cropping tightly to head-and-shoulders deletes background pixels — every pixel deleted is budget the face keeps.

If you need exactly 20 KB for a signature, that is 20 × 1024 = 20 480 bytes. UnderKB’s byte counter is the real server number, not the rounded Explorer number.

4 · What costs what: quality search vs shrinking dimensions

Faces tolerate quality loss better than text. A 600 × 800 portrait at quality 55 still looks fine at 100 KB. An A4 marksheet at quality 55 looks like a smear — for text, keep quality high and drop DPI or switch to greyscale instead.

Re-encoding a JPEG always loses a generation. If your file is already 48 KB and the cap is 50 KB, do not touch it. Re-compressing “for safety” only removes detail.

5 · JPEG vs WebP vs PNG — what portals actually accept

Rule of thumb: if you are uploading to a government form, output JPEG. If you are emailing, embedding on a website, or archiving, WebP at the same byte count looks dramatically better. UnderKB’s Convert page does the re-encode in one pass.

6 · PDF caps: DPI to KB, and the signed-PDF trap

Source beats compressor: a 600 DPI scan squeezed to 200 KB destroys exactly the glyphs you scanned. Re-scan at 150–200 DPI instead — same cap, far more legible text.

Signed or encrypted PDFs must never be re-encoded. Compression invalidates the signature’s byte seal and cannot open encrypted files. Compress the unsigned original, then sign the compressed file. This applies to the 200 KB PDF and 300 KB PDF pages.

7 · Per-portal master spec table — the single source of truth

Specs shift every notification cycle. This table targets the strictest common case. When the notification publishes a range, use UnderKB’s Maximum + Minimum fields to land inside the band, not merely under the ceiling.

8 · Checklist before you hit Upload

1. Check format, dimensions, range, background — in that order.
2. Fix cm and px first with Passport size photo or Photo maker; compress second.
3. Crop to head-and-shoulders; eyes in top third; no shadow across the face.
4. Shoot against plain white wall in daylight; no cream, no grey.
5. Choose JPEG for photo fields, transparent PNG only for signature fields.
6. Set Maximum to the ceiling and Minimum to the floor when a band is published (e.g. 50 and 20 for SSC).
7. Check the byte counter shown — that is the real validator number (Explorer rounds).
8. If the file is already under the cap and in the right format/pixels, do not re-encode.
9. For A4 scans: greyscale at 150 DPI before any PDF compression; re-scan rather than squeeze a 600 DPI source.
10. Keep the original for print. Upload the compressed copy only where the cap applies.

Next steps: jump to the exact cap you need — 20 KB · 50 KB · 100 KB · 200 KB · 300 KB · PDF 200 KB — or use any-size compressor to type any number.