online lookup

ISO 8583 Bitmap Calculator (Both Directions)

Works both ways: fields in, bitmap out — or bitmap in, fields out, with all 64/128 bits drawn.

Fields → bitmap

The secondary bitmap is handled for you: using any field 65–128 sets bit 1 automatically.

Bitmap (hex)：—

Bitmap → fields

Accepts 16 or 32 hex characters. Bit 1 set means a secondary bitmap follows.

Fields present：—

How to read a bitmap

The bitmap tells the receiver which data elements are present. The primary bitmap is 8 bytes, 64 bits, one per field, and you count from bit 1, not bit 0 — the off-by-one that catches almost everyone once.

Bit 1 is special: setting it means a secondary bitmap follows, covering fields 65–128. So the moment you use any field above 64, bit 1 must be set and the bitmap grows from 8 bytes to 16. The calculator above handles that for you.

Checking it by hand

Take the first hex character: 7 is binary 0111, so bit 1 is clear (no secondary bitmap) and bits 2, 3 and 4 are set (DE2, DE3 and DE4 present). One hex character is four bits — carry on that way and you can verify any bitmap manually.

When a message fails to parse, look at the bitmap first. If the field list comes out obviously wrong — a scatter of high-numbered fields that shouldn't be there — the encoding guess is usually what's wrong. The same bytes read as ASCII and as BCD produce completely different bitmaps. That's exactly what the parser's auto-detection scores on.

Common traps

Don't count the bitmap itself as DE1. DE1 is the secondary-bitmap indicator, not a data element in its own right, which is why the reverse lookup above never lists field 1. And match the bitmap length to the encoding: 16 characters represent 8 bytes under ASCII, whereas under binary encoding those 8 bytes are the bitmap itself.