A wire's cut length is the sum of the branch lengths along its route, plus an allowance at each end (from the dimension point to the end of the terminal, strip length included), plus any service loop, then slack or twist take-up, rounded up. For a wire routed 800 mm between two connectors with 20 mm per end, that is 840 mm.
The rule
- Route. Follow the wire through the branch tree from one end to the other and add the branch lengths it passes through.
- End allowances. Add, at each end, the distance from the drawing's dimension point to where the wire ends inside the terminal. For a connector this depends on the housing and terminal; for a splice it is the length needed to make the joint.
- Service loops. Add any extra length the drawing asks for at a connector.
- Slack and twist. Add a percentage for slack if your process uses one; twisted pairs need take-up, usually a percentage with a minimum.
- Round. Round up to your cutting step, for example 5 mm.
- Fixed lengths. If the customer fixes a wire's length, use it — and check that it still reaches along its route.
Worked example
Our test harness F2 has three connectors and one splice. With 20 mm per connector end, 10 mm per splice end and rounding up to 5 mm:
| Wire | Route | Bare route length | + allowances | Cut length |
|---|---|---|---|---|
| W1 | X1 → X2 | 800 mm | +20 +20 | 840 mm |
| W2 | X1 → X3 | 653 mm | +20 +20 = 693 | 695 mm (rounded) |
| W3 | X1 → splice | 300 mm | +20 +10 | 330 mm |
| W4 | splice → X2 | 500 mm | +10 +20 | 530 mm |
| W5 | splice → X3 | 353 mm | +10 +20 = 383 | 385 mm (rounded) |
In our tests on 30–31 October 2026, three browser tools gave the bare route lengths (800, 653, 300, 500, 353 mm) as cut lengths. Built that way, every wire is short by the length it needs inside its terminals.
Where to measure from
Drawings dimension branches to different points: the connector's back face, its mating face, or the centre of a breakout. Decide which one your allowances are measured from, write it on the drawing template, and keep it the same for every customer. Length tolerances are the customer's or the applicable standard's; IPC/WHMA-A-620 covers them in its section on measurement.
In Zorowire
Cut lengths are computed from the branch tree with your shop's rules: connector and splice allowances (20 mm and 10 mm by default), service loops, slack, twist take-up and rounding. A jacketed cable gets one cut length for all its cores. A customer-fixed length replaces the result, and a finding tells you if it cannot reach. Change a branch and every wire through it changes in the cut list.
Questions
Why are my wires short when I cut them to the drawing?
Probably because the cut length is the bare branch sum. Each end needs extra length to reach into the terminal, including the stripped part.
What end allowance should I use?
It depends on the housing, the terminal and where your drawing dimensions from. Start from your bench's practice and the terminal's application specification; 20 mm per connector end is only our editable default.
How do I handle twisted pairs?
Twisting shortens the pair, so add take-up: a percentage of the length, with a minimum. Set it from a measured sample of your own twisting.
Sources
- Zorowire test fixture F2 (5 wires, 3 connectors, 1 splice) and the cut lengths each tool produced — Zorowire test or research, 2026-10-31
- Zorowire hands-on test of harness.design (Free plan, fixture F2) — Zorowire test or research, 2026-10-30
- Zorowire hands-on test of HarnessHive (trial, fixture F2) — Zorowire test or research, 2026-10-30
- Zorowire hands-on test of Splice CAD, web app (fixture F2) — Zorowire test or research, 2026-10-31
- IPC/WHMA-A-620E table of contents (free preview) · retrieved 2026-10-30
Stuck on something else? Ask the community.
Ask a questionNew harness guides in your inbox
About one e-mail a month: new guides, answers to the questions shops ask, and Zorowire news.
