How to size a signature for bank and exam forms

What a signature upload actually requires

Banks and exam bodies do not want a photo of you signing. They want a clean, high-contrast image of the ink itself. Three things decide whether it is accepted: the ink and paper, the shape (signatures are landscape, wider than tall), and the file weight in kilobytes. Get those right and the format choice almost always falls out as a plain JPG.

• Use black or dark-blue ink on plain, unlined white paper. Black gives the strongest contrast and survives compression best; some bodies insist on it, so use black when in doubt.
• Sign at a normal size with a medium-tip pen, because a thin gel pen can vanish once the image is shrunk to 15 KB.
• Aim for a landscape rectangle roughly twice as wide as it is tall: about 4.0 × 2.0 cm, or 140 × 60 px for portals that measure in pixels.
• Leave a small even margin of white around the ink. Touching the edges or a slanted scan are common reasons a form flags the signature as 'not clear'.

Common signature specs at a glance

The table collects the dimensions, file-size ceilings and formats most commonly requested. Bank specimen forms are looser than exam portals, which enforce a hard KB cap the moment you upload.

Reading the spec: cm, pixels and KB

Forms describe the same signature in three different units, which is where the confusion starts. Once you can translate between them, every requirement becomes a quick recipe.

Centimetres vs pixels

A form asking for "4.0 × 2.0 cm" means a physical print size, which only becomes a fixed pixel count once you pick a DPI. At 300 DPI that works out to about 472 × 236 px. A form asking for "140 × 60 px" means the literal pixel grid and ignores DPI entirely. If your spec is in centimetres, resize to the pixel equivalent and you are safe.

File size in KB

KB is the weight of the saved file, separate from its dimensions. A 140 × 60 px signature can be 6 KB or 40 KB depending on JPEG quality and how much white space surrounds the ink. When a form says "10–20 KB", that is the weight it checks, so you compress to land inside that band without changing the pixel size. Signatures are small images, so the usual challenge is staying under a low ceiling, not adding weight.

Scanning vs photographing your signature

Both work. A flatbed or document scanner gives the cleanest result; a phone camera is fine if you control the light. The goal either way is dark ink on a flat, evenly-lit white field with no shadow.

If you use a scanner

• Scan at 200–300 DPI in colour or greyscale. Higher DPI only adds weight you will compress away.
• Lay the paper flat against the glass so the signature is not skewed.
• Save as JPG. If your scanner outputs PDF, you can convert the page later, but a direct JPG is simpler.

If you use your phone

• Shoot in bright, even daylight near a window, and avoid the camera flash, which leaves a hot spot and a hard shadow.
• Hold the phone directly above the paper, parallel to it, so the rectangle stays square and not trapezoidal.
• Keep your own shadow and the phone's shadow off the page; lift the phone rather than leaning over the sheet.
• Many iPhones save photos as HEIC, which several portals reject; if so, convert it to a standard JPG before you size it.

Either way you will capture far more page than you need. The next step is to crop down to only the ink.

Crop, resize and compress, step by step

This is the core workflow. Do it in order: a tight crop first makes the resize and compress steps far easier to hit, because there is no wasted white area inflating the file.

1. Note four things from the form: the dimensions, the KB range, the required format, and whether a separate scan or PDF is allowed.
2. Crop tight to the ink, leaving a thin, even white margin all round. This removes the page edges and any stray marks and centres the signature.
3. If the spec is in centimetres, convert to pixels (about 472 × 236 px for 4.0 × 2.0 cm at 300 DPI) and resize to those exact pixels; if it is already in pixels, resize straight to that.
4. Compress to just under the top of the KB range. For a 10–20 KB form, aim for roughly 18 KB so a re-save by the portal does not push you over the cap.
5. If the file lands under the minimum KB after compression, pad it back up until it clears the floor without altering how the signature looks.
6. Confirm the file is JPG, then upload, and keep the original scan in case a correction window opens later.

Hitting a tight KB limit without losing the ink

The narrowest signature limits (4 KB on some NTA forms, 10 KB elsewhere) are where people over-compress and end up with a grey, broken signature the form calls 'not clear'. A few habits keep it legible.

• Crop out white space before compressing. A signature that fills the frame compresses to a lower KB at the same visible quality than one floating in a large white border.
• Greyscale or pure black-and-white versions of the ink are lighter than colour, and a black signature loses nothing by dropping colour data.
• Resize the pixel dimensions down to what the form needs before compressing, because a 140 × 60 px image is naturally tiny, so it hits 10 KB without aggressive quality cuts.
• If you must choose between a slightly larger file and a faded signature, keep it legible. A signature flagged as unreadable is rejected as firmly as one that is over the limit.

For the matching photo on the same form, plus the full per-exam dimension and KB tables, see the exam photo and signature size guide.

Keeping a consistent specimen signature

Banks store a specimen signature when you open an account and compare every cheque and KYC update against it. An exam application is one-off, but your bank signature follows you for years, so consistency matters more than it does anywhere else.

• Sign the way you naturally do day to day, not a fancier version you cannot reliably repeat. The version on file should be the one you can reproduce on a cheque under pressure.
• Avoid all-capital-letter signatures where you can; some banks and exam bodies reject them, and they are easier to imitate.
• Keep one clean digital copy of your signature saved at home so future online forms reuse the same image instead of a fresh, slightly different scan each time.
• If you have genuinely changed your signature, update the specimen at the branch rather than letting cheques and KYC drift out of sync, because a mismatch can get a cheque returned.

Why signature uploads get rejected

If you are unsure which message maps to which fix, the fix upload errors page walks each one through with the right tool already loaded, and the why forms reject photos guide explains the full set of causes in plain language.