Core inputs only — quick sizing with engineering defaults.
Inputs (SI units)
From cable datasheet
If unsure, leave and use the recommended standard size below
Results
Fill percentage
61.44 %
Max allowed 40% for 6 cable(s)
Total cable area
301.6 mm²
Conduit internal area
490.9 mm²
Compliance
FAIL
Next standard conduit (if needed)
32 mm
Upsize required
Jam ratio
3.13
N/A (only 3-cable runs are jam-critical)
✕ FAIL — Fill (61.44 %) EXCEEDS the applicable 40% limit for 6 cable(s) — use 32 mm conduit.
Engineering Recommendations
→Upsize to 32 mm conduit — required to bring fill within the 40% limit.
→Avoid exactly-3-cable pulls at jam ratio 2.8–3.2; add a 4th cable/spacer or change conduit size.
→Engineering-grade preliminary calculation. Final design must be verified against project-specific site conditions, manufacturer datasheets, applicable standards and utility requirements.
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Engineering Formula
A_cables = N × π × d² / 4
A_conduit_min = A_cables / fill%
d_conduit = √(4 × A_conduit / π)
NEC Chapter 9 caps fill at 53% for one cable, 31% for two, 40% for ≥3. IS 732 uses similar limits.
Step-by-step Calculation
1.Cross-sectional area per cableπ×OD²/450.27 mm²
2.Number of cablesN6
3.Total cable areaN × A_cable301.6 mm²
4.Conduit internal areaπ×ID²/4490.9 mm²
5.Applicable max fill (NEC Ch.9 style)1 cable→53%, 2→31%, 3+→40%40 %
6.Actual fill percentageA_cables / A_conduit × 10061.44 %
7.Minimum conduit ID for compliant fill√(4×A_cables/(fill%×π))31 mm → 32 mm standard
8.Jam ratio (conduit ID / cable OD)ID/OD3.13 (jam ratio only critical for exactly 3 cables)
How to use this calculator: Conduit Fill
Conduit size for cable bundle at 40% fill. The example below is calculated by this page's real engine from the displayed inputs.
1Confirm that the Conduit Fill matches the quantity or design check you need.
2Enter Cable outer diameter, Number of cables, and Conduit internal diameter using the units printed beside each field.
3Select the applicable Cable type options; these choices change the calculation method or factors.
4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.
Input guide and example values
Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.
Input
Example value
Why it matters
Cable type
PV DC single-core (thick jacket)
Select the option that matches the real installation or scenario.
Cable outer diameter
8 mm
From cable datasheet
Number of cables
6 -
Measured or known number of cables used by the calculation engine.
Conduit internal diameter
25 mm
If unsure, leave and use the recommended standard size below
Formula inputs & variables for Conduit Fill
These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.
Variable / input
Unit
Meaning in this calculation
Cable type
—
Select the option that matches the real installation or scenario.
Cable outer diameter
mm
From cable datasheet
Number of cables
-
Measured or known number of cables used by the calculation engine.
Conduit internal diameter
mm
If unsure, leave and use the recommended standard size below
How the Conduit Fill works
The Conduit Fill uses Cable type, Cable outer diameter, Number of cables, and Conduit internal diameter to calculate Fill percentage, Total cable area, Conduit internal area, Compliance, Next standard conduit (if needed), and Jam ratio. Its engine applies A_cables = N × π × d² / 4; the worked values below come from that same live calculation rather than a separately typed example.
With Cable type PV DC single-core (thick jacket), Cable outer diameter 8 mm, Number of cables 6 -, and Conduit internal diameter 25 mm, the main worked-example result is Fill percentage = 61.44 %.
How each Conduit Fill input is used
Cable type
The Conduit Fill worked example selects “PV DC single-core (thick jacket)”. Available choices include PV DC single-core (thick jacket) and Building wire (THHN-type). This selection may change the method or factor used by the engine, so choose the option that matches the real case.
Cable outer diameter
The Conduit Fill worked example uses Cable outer diameter = 8 mm. This value is passed directly into the calculation, with an allowed minimum 1. From cable datasheet
Number of cables
The Conduit Fill worked example uses Number of cables = 6 -. This value is passed directly into the calculation, with an allowed minimum 1.
Conduit internal diameter
The Conduit Fill worked example uses Conduit internal diameter = 25 mm. This value is passed directly into the calculation, with an allowed minimum 5. If unsure, leave and use the recommended standard size below
Conduit Fill formulas and result interpretation
Formula 1: relationship used
In the Conduit Fill, A_cables = N × π × d² / 4. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.
Formula 2: relationship used
In the Conduit Fill, A_conduit_min = A_cables / fill%. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.
Formula 3: relationship used
In the Conduit Fill, d_conduit = √(4 × A_conduit / π). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.
Fill percentage
For the displayed Conduit Fill worked example, Fill percentage is 61.44 %. Max allowed 40% for 6 cable(s) Verify Cable type, Cable outer diameter, and Number of cables and their units before relying on this output.
Total cable area
For the displayed Conduit Fill worked example, Total cable area is 301.6 mm². Verify Cable type, Cable outer diameter, and Number of cables and their units before relying on this output.
Conduit internal area
For the displayed Conduit Fill worked example, Conduit internal area is 490.9 mm². Verify Cable type, Cable outer diameter, and Number of cables and their units before relying on this output.
Compliance
For the displayed Conduit Fill worked example, Compliance is FAIL. Verify Cable type, Cable outer diameter, and Number of cables and their units before relying on this output.
Next standard conduit (if needed)
For the displayed Conduit Fill worked example, Next standard conduit (if needed) is 32 mm. Upsize required Verify Cable type, Cable outer diameter, and Number of cables and their units before relying on this output.
Jam ratio
For the displayed Conduit Fill worked example, Jam ratio is 3.13. N/A (only 3-cable runs are jam-critical) Verify Cable type, Cable outer diameter, and Number of cables and their units before relying on this output.
Conduit Fill accuracy, checks and limitations
Conduit Fill units check: confirm Cable type, Cable outer diameter (mm), Number of cables (-), and Conduit internal diameter (mm) before calculating.
Conduit Fill result check: compare Fill percentage, Total cable area, Conduit internal area, Compliance, Next standard conduit (if needed), and Jam ratio with the substituted formula steps and the displayed rounding precision.
Conduit Fill: Use this result for preliminary design and cross-checking. Confirm the applicable code edition, manufacturer data, site conditions and qualified-engineer approval before final design or installation.
Understanding the result
Read the main result together with supporting checks, assumptions, limits and intermediate values.
For a manual check, repeat the first equation, confirm the units and change one input at a time.
Common mistakes when using Conduit Fill
Do not mix units for Cable outer diameter (mm), Number of cables (-), Conduit internal diameter (mm). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
Do not leave Cable type on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
Do not replace the displayed A_cables = N × π × d² / 4 relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
Do not treat Fill percentage = 61.44 % from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.
When the Conduit Fill is useful
Conduit Fill is designed for cases where Cable type, Cable outer diameter, Number of cables, Conduit internal diameter are known and you need Fill percentage, Total cable area, Conduit internal area. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.
Use the calculator for the scope described by its inputs and notes. The displayed method is A_cables = N × π × d² / 4. If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.
Cable type and Cable outer diameter: what changes the answer
The worked example uses Cable type = PV DC single-core (thick jacket), Cable outer diameter = 8 mm, Number of cables = 6 -, Conduit internal diameter = 25 mm. With those values, Fill percentage is 61.44 %. Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.
For this calculator, the main input roles are: Cable type: Select the option that matches the real installation or scenario. Available choices include PV DC single-core (thick jacket), Building wire (THHN-type). Cable outer diameter (mm): From cable datasheet Number of cables (-): Measured or known number of cables used by the calculation engine. Conduit internal diameter (mm): If unsure, leave and use the recommended standard size below
How to sanity-check a Conduit Fill result
Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Fill percentage, because it is the first worked-example output shown by the live engine.
Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.
Next logical calculator
Continue with Solar Plant Earthing Design Calculator
Solar Plant Earthing Design Calculator covers the same practical workflow from a related calculation angle, making it a useful cross-check after Conduit Fill.
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