How to scan your signature with a phone
The signature is the one document every exam asks for. SSC and RRB no longer let you upload a photo — it is captured live — but you still upload a signature. And a bad signature scan is one of the top reasons for rejection.
You do not need a scanner. A phone camera is enough if you do five things right.
What you need
- A plain white A4 sheet (no lines, no stains). Printer paper is perfect.
- A black gel pen or a black ball pen that writes dark. Most notices say black ink; banking accepts black, RRB asks for black.
- Daylight from a window, or a bright room light.
- Your phone.
Avoid blue ballpoint if you can. It turns pale grey after compression and some portals reject faint signatures.
Step 1: Sign properly
- Sign in your normal running signature — the one you will also sign at the exam centre. If it differs on the day, you can be stopped.
- Do not sign in capital letters. IBPS, SBI and RBI notices say this clearly. A signature in block capitals is treated as invalid.
- Sign bigger than usual — about 6–8 cm wide. A bigger signature keeps its detail when it is shrunk to 140 × 60 pixels.
- Sign two or three times on the sheet. Pick the cleanest one later.
Special formats
- UPSC (CSE, NDA, CDS): sign three times, one below another, and capture all three in one image. The final image is square, 350–500 px, 20–100 KB.
- Bihar Police Constable: two separate signature files — one in Hindi, one in English, each 15–25 KB.
- RRB: the signature should sit centred in a 35 × 20 mm box. Sign so it fits in a box of that shape.
Step 2: Light it right
The goal is pure white paper and pure black ink, with no shadow.
- Put the sheet on a flat table near a window.
- Hold the phone directly above the paper, parallel to it. A tilted phone makes the signature look slanted.
- Check that your hand or phone is not casting a shadow on the signature. Move to the side of the light if needed.
- Turn the flash off. Flash makes a shiny spot in the middle.
Step 3: Take the photo
- Fill most of the screen with the signature, leaving a small margin.
- Tap on the signature to focus. Wait a second before you click.
- Take two or three photos. Zoom in on the phone and pick the sharpest.
Do not use the phone’s document-scanner mode with heavy filters. It sometimes eats the thin parts of the signature.
Step 4: Clean, crop and resize
Open Signature Resize on SahiSize, or go straight to your exam page.
- Pick your photo. It stays on your phone.
- Crop tight. Leave only a thin white border. The ink should fill at least 80% of the box width. SSC specifically rejects signatures that are too small inside the image.
- Clean. The cleanup option makes the paper pure white and the ink dark, and removes grey shadows.
- Resize to your exam. Pick the exam and SahiSize sets the pixels and KB.
- Check the ticks — KB, pixels and format all green — and download.
Signature sizes for common exams
Always check the latest official notice — these are the values from recent notices.
| Exam | Pixels | KB |
|---|---|---|
| IBPS PO, SBI, RBI | 140 × 60 px | 10–20 KB |
| SSC CGL, CHSL, MTS, CPO | 6.0 × 2.0 cm ≈ 472 × 157 px at 200 DPI | 10–20 KB |
| RRB ALP, Group D, NTPC | at least 140 × 60 px | 30–49 KB |
| NEET UG, JEE Main | KB only | 10–100 KB |
| CUET UG, UGC NET | KB only | 10–50 KB |
| UPSC CSE | 350–500 px square (3 signatures) | 20–100 KB |
| CTET | 3.5 × 1.5 cm | 3–30 KB |
SSC gives only centimetres. At 200 DPI, 6.0 × 2.0 cm works out to about 472 × 157 pixels — that is what SahiSize uses by default.
The RRB problem: signature too small in KB
RRB wants 30–49 KB. A clean black-on-white signature is so simple that it often compresses to only 10–15 KB, even at full quality. Then the portal says the file is too small.
You do not need to fake it by adding noise yourself. SahiSize’s RRB preset handles it: it first uses the highest quality, then a larger pixel size within the allowed range, and only if needed adds a very faint grain or white padding. The signature looks the same, and the file reaches 30 KB.
Common mistakes
- Signature on lined or ruled paper. The lines show up. Use plain paper.
- Photo of the screen. Never photograph a signature shown on another screen; it becomes blurry with moiré lines.
- Using an old signature image. If you signed differently three years ago, make a fresh one.
- Wrong orientation. The image must be landscape (wider than tall) for most exams, except UPSC which is square.
- Saving from WhatsApp. WhatsApp re-compresses images. Transfer by cable or use the original file.
FAQ
Can I sign on paper with blue ink?
Some exams allow blue, but black is safer: it stays dark after compression. RRB and SSC prefer black. Check your notice.
Can I use a digital signature drawn on the screen?
No. Exams want your handwritten signature on paper, photographed or scanned. A finger-drawn signature looks different from how you sign at the centre.
My signature is very small. Will it still work?
Crop tightly so the ink fills the box. If it looks thin and broken after resizing, sign again bigger with a thicker pen.
Is my signature uploaded anywhere?
No. SahiSize processes everything inside your browser. Nothing is sent to our server. SahiSize is not affiliated with any exam body.
Next: How to make a thumb impression and handwritten declaration format.