Conduit Jam Ratio Calculator
Screen three or more identical round cables for published jamming-risk ranges and verify conduit fill. New here? Read the quick guide.
Project details (optional)Add details
Conduit and cable inputs
Configure the proposed pull
There is no single ideal number. Avoid the principal published risk range when practical, and always verify that conduit fill passes.
Practical summary: ratios below 2.6 or at least 3.1 fall in lower published risk ranges; 2.6–<2.8 and 3.0–<3.1 are moderate; 2.8–<3.0 is the principal range to avoid. A lower-risk ratio is not approval to exceed permitted fill.
Pull cross-section
Identical cables inside the conduit
Select a cable to draw the proportional pull cross-section.
Calculated result
Jamming and conduit-fill details
The published risk ranges apply to three or more identical cables. Mixed cable diameters require a detailed pulling analysis rather than this simplified ratio.
Export this jamming-risk calculation
Create a field-ready record containing the selected conduit and cable, quantity and fill check, jam ratio, published risk range, formula, and project details.
Select a cable and enter at least three identical cables before exporting a report.
Cable pulling guidance
Use jam ratio as one part of pull planning
Published manufacturer guidance defines jam ratio as conduit inside diameter divided by cable outside diameter. The risk ranges are intended for three or more identical round cables and account for the oval cross-section encountered at conduit bends.
What is a cable jam ratio?
Jam ratio is the conduit inside diameter divided by the outside diameter of one identical round cable. It screens whether three or more cables fall within a published jamming-risk range.
Does a low-risk result guarantee a successful pull?
No. Pulling tension, sidewall pressure, bends, lubricant, cable construction, measured diameter, and pathway condition must also be evaluated.
Can I use different cable sizes together?
The simplified risk ranges are intended for identical round cables. Mixed diameters require a more detailed pulling analysis.
Why does cable quantity not change the jam ratio?
Jam ratio uses only conduit inside diameter and one cable's outside diameter, so it does not change once three or more identical cables are entered. Quantity does change conduit fill. The calculator therefore evaluates fill separately and displays Does not fit whenever the entered quantity exceeds permitted capacity.
What jam ratio should I aim for?
There is no single ideal number because the risk ranges are not linear. Ratios below 2.6 or at least 3.1 fall in lower published risk ranges, 2.6 to below 2.8 and 3.0 to below 3.1 are moderate, and 2.8 to below 3.0 is the principal range to avoid. Conduit fill must still pass, and a lower-risk range does not guarantee a successful pull.
Review the complete calculation approach on the methodology page.