Bend & Tension · Free · Same math as the app

Cable Bend Radius Calculator

Is this bend too tight? Enter the cable type, its outside diameter and the radius you measured, and get the minimum bend radius for that cable, checked against your bend.

Bend radius

2.00"min 1.20" (4× OD)

WITHIN SPEC

Installed, no load (4× OD)1.20" / 30 mm

Installed, no load (4× OD): 1.20" / 30 mm
Under load, pulling (4× OD): 1.20" / 30 mm
Min bend diameter: 2.40"
Max pull tension: 25 lbf (110 N) per TIA-568 for 4-pair

Ratios per ANSI/TIA-568 and TIA-569 general practice. Radius is measured to the INSIDE of the bend, not the centreline. Manufacturer limits override these and are sometimes tighter on armored and small-count fiber.

Make the Printout

Opens this in the VoltIQ app with your numbers. Add your name and the job, then save it or send it to the crew.

No signal needed

This page needs signal. The app doesn't.

In the riser, the basement or above the ceiling, VoltIQ runs this calculation with no bars. Then it puts the answer on a Printout with your name on it.

Open in the web app

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Join the phone pilot

How it works

Pick the cable type and enter its outside diameter. The minimum bend radius is that diameter times a multiple set by the cable type. 4-pair UTP / horizontal: 4× OD, installed or pulling. Multipair backbone and coax: 10× OD, installed or pulling. Optical fiber: 10× OD installed, 20× OD while pulling.

Then measure the bend and enter its radius, to the inside of the curve, not the centreline. The calculator compares it with the installed minimum. A cleared field, or a zero, gets a message under the field and no result.

The last field asks whether the ties are over-cinched. The app's rule is hand-tight only: a tie should slide along the bundle.

The calculator opens on 4-pair UTP / horizontal at 0.300" with a 2.00" bend. The installed minimum is 1.20" (30 mm), so it reads WITHIN SPEC. Tighten the same bend to 1.00" and it reads TOO TIGHT, with the fix “Open the bend to at least 1.20" (30 mm) at the inside of the curve.”

Reading the result

The big number is the radius you measured, next to the minimum it's judged against and the multiple behind it. The stamp beside it is one of three.

WITHIN SPEC: the measured radius is at or over the installed minimum.
MARGINAL: under the minimum, but at 85% of it or more. It's still under: it carries a WON'T PASS line and the fix.
TOO TIGHT: under 85% of the minimum.

On the opening cable, with its 1.20" minimum, 1.02" reads MARGINAL and 1.01" reads TOO TIGHT.

Under that are the working figures: the installed minimum in inches and millimetres, the minimum while pulling, the minimum bend diameter (twice the installed radius), and the max pull tension line for the cable type.

WON'T PASS, WON'T LAST, JUST UGLY

Each concern is filed under one of three tags, with its math underneath.

WON'T PASS shows whenever the radius is under the installed minimum, MARGINAL or TOO TIGHT. On copper a tight bend shows up as return loss; on fiber, as attenuation a tester will find. The math gives the measured radius against the minimum.
WON'T LAST shows whenever you answer Yes to over-cinched ties. Over-cinched ties deform the jacket and crush pair geometry: the fault that tests fine on day one and drifts a year later. It doesn't change the stamp. The opening example with ties over-cinched still reads WITHIN SPEC.
JUST UGLY shows when the bend is within spec but under 1.5 times the minimum, and the ties are fine. The math gives the radius as a multiple of the diameter. A 1.50" bend on the opening cable reads WITHIN SPEC with 5.0× OD installed. With the ties over-cinched, the WON'T LAST line shows instead.

What it doesn't check

Pull tension. Nothing is calculated. The max pull tension line is fixed per cable type: 25 lbf (110 N) per TIA-568 for 4-pair for 4-pair UTP / horizontal, and the manufacturer's figure for the others. The diameter doesn't change it.
The pulling radius. The under-load figure prints for reference and is never judged. Optical fiber at 0.200" has a 2.00" (51 mm) installed minimum and 4.00" (102 mm) while pulling. A 3.50" bend reads WITHIN SPEC, under the pulling figure.
The manufacturer's limit. The ratios follow ANSI/TIA-568 and TIA-569 general practice. Manufacturer limits override them, and are sometimes tighter on armored and small-count fiber.
The rest of the run. It checks the one bend you measured. It doesn't count bends or look at the length. For how many cables fit the raceway, use the conduit fill calculator.

Questions

What's the minimum bend radius for Cat6 and Cat6A?

Cat6 and Cat6A UTP are 4-pair cable: 4 times the cable's outside diameter once installed, measured to the inside of the bend. A 0.300" cable needs 1.20" (30 mm).

What's the minimum bend radius for fiber?

10 times the cable's outside diameter installed, and 20 times while pulling. A 0.200" cable needs 2.00" (51 mm) installed and 4.00" (102 mm) under load. The calculator judges the installed figure. Manufacturer limits override these, and are sometimes tighter on armored and small-count fiber.

Do I measure to the inside of the bend or the centreline?

To the inside of the bend. The minimum the calculator gives, and the fix it suggests, are both at the inside of the curve.

What's the max pull tension for 4-pair cable?

The app prints 25 lbf (110 N) per TIA-568 for 4-pair. It's a fixed reference line, not a calculation: the diameter doesn't change it. For multipair backbone, optical fiber and coax it points to the manufacturer's figure.

Do over-cinched ties fail the bend?

No. They add a WON'T LAST line and leave the stamp alone, so a bend can read WITHIN SPEC with it. Over-cinched ties deform the jacket and crush pair geometry: it's the fault that tests fine on day one and drifts a year later. Hand-tight only: a tie should slide along the bundle.