Use product dimensions, not a diameter shortcut
This model uses IPEX's Scepter rigid PVC coefficient of 0.054 mm per metre per °C. It does not apply to other conduit materials or automatically to another manufacturer's PVC. Supply the actual fitting's rated travel and fully compressed setting length.
Confirm design temperatures, available movement, mounting and temperature suitability from the applicable product instructions. The calculator does not infer weather, sun exposure, operating temperature limits or code requirements. Inputs and results stay in the page and are not saved or transmitted.
Method and worked example
Run movement ΔL = 0.054 × run length in m × (maximum − minimum temperature in °C), giving mm. The travel-based count is ceil(ΔL ÷ rated fitting travel). It is a capacity calculation for identical fittings, not a routing plan.
Piston extension = rated travel × (maximum − installation temperature) ÷ (maximum − minimum). Total setting length = fully compressed length + extension. At the minimum temperature the model uses full extension; at the maximum it uses zero extension.
Example: 30 m from −20°C to 40°C gives 97.2 mm total movement. For a verified 101.6 mm travel and 215.9 mm compressed length, installation at 10°C gives one joint by travel, 50.8 mm piston extension and 266.7 mm total setting length. These are an illustrative scenario; verify the actual part dimensions before use.
The arithmetic retains precision; display rounds to three decimals or scientific notation. The fitting count is always rounded upwards. A zero or reversed temperature span is rejected because the setting ratio would be undefined or invalid.
What the count and setting do not decide
The count assumes the stated run movement can be assigned to the identical fittings. Actual anchors, supports, elbows, branches and friction determine where movement occurs. The calculation does not distribute lengths between fittings or provide an anchoring, support-spacing or installation procedure.
Use the same relevant temperature conditions for the run and fitting. This linear model does not predict local temperature gradients, material suitability, loads on fittings, restraint stresses or movement from structural changes. A plausible number is not evidence of acceptable equipment or code compliance.
Common questions
Is piston extension the full setting length?
No. Extension is the variable portion above the fully compressed setting. The full measurement in this model adds your verified compressed length. Use the manufacturer's measurement reference for that particular fitting.
Can I divide a long run by the displayed count and place joints anywhere?
No. Count alone does not define an arrangement. Movement must reach each fitting as intended; follow the manufacturer's directions for placement, supports and fixed points.
Why are there no preset fitting dimensions?
Nominal conduit size does not uniquely establish the installed fitting's dimensions. Enter data from the actual part's drawing so the calculation uses the correct travel and compressed measurement.
Related tools
Source
IPEX, Electrical Products Catalogue — Canada, Scepter technical information, printed pages 12–13: linear coefficient, total-movement allowance, fitting-count method and piston-setting relationship. Checked November 10, 2026. The required actual fitting dimensions remain explicit inputs.
Report a problem or suggest a source; your dimensions are not attached automatically.