RoundLot (FIX tag 561)

QtyFIX 4.4

RoundLot (tag 561) is a Qty field defined in FIX 4.4. It appears in 2 message types, always optionally.

At a glance

Tag: 561
Name: RoundLot
Datatype: Qty (float)
Dialects: FIX 4.4
Messages: 2

What the specification says

The trading lot size of a security

Descriptions are quoted from the FIX Orchestra sources under the Apache 2.0 licence.

A real message using tag 561

SecurityDefinition · FIX 4.4

Tag	Field	Wire value	Meaning
8	BeginString	FIX.4.4
9	BodyLength	105
35	MsgType	d	Security Definition
49	SenderCompID	BOARTEAM
56	TargetCompID	COUNTERPARTY
34	MsgSeqNum	2
52	SendingTime	20240101-12:00:00.000
320	SecurityReqID	EXAMPLE
322	SecurityResponseID	EXAMPLE
323	SecurityResponseType	1	Accept security proposal as is
561	RoundLot	1000000
10	CheckSum	001

Edit and decode it yourself

Shown with | separators for readability. On the wire FIX uses SOH (0x01), an invisible control byte — and because BodyLength and CheckSum are computed over the actual bytes, the two forms have different checksums. Both are valid and both decode here.

Open in the full decoder →

Generated from the FIX 4.4 dictionary and verified at build time: it parses and validates with no issues. Open the decoder to try your own message.

Where tag 561 appears

Requiredness is a property of the message, not of the field: the same tag can be optional in one message and conditionally required in another.

Message	MsgType	Requiredness	Where in the message
SecurityDefinition	d	Optional	directly on the message body
SecurityList	y	Optional	inside the SecListGrp component

Wire format

A decimal quantity. Fractional quantities are legal, which is why this is a float family rather than an integer. @boarteam/fix parses the value as a number and reports parse/invalid-float when it does not lex as one; the raw string is kept so precision and trailing zeros are never lost.

Read tag 561 in TypeScript

decode.tsts

import { createFixEngine } from "@boarteam/fix";import { dictionary } from "@boarteam/fix-dict-fix44";const fix = createFixEngine(dictionary);const { message, issues } = fix.parse(raw);const field = message.fields[561];field?.name;   // "RoundLot"field?.raw;    // the verbatim wire stringfield?.value;  // coerced to a number

Decode this in your own code

The same engine that produced the decoded example above is an Apache-2.0 npm package with zero runtime dependencies. It runs in Node and in the browser, and parse() returns problems as data instead of throwing.

npm i @boarteam/fix @boarteam/fix-dict-fix44

Try the decoder Source on GitHub