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The inside diameter of the seal-off fitting's bore.
This is the internal bore diameter of the conduit seal-off fitting, not the conduit's trade size.
The length of the fitting's sealing chamber to be filled with compound.
Measure the length of the cavity that the sealing compound must fill, per the fitting manufacturer's specifications.
Sealing compound volume needed
0.0068 gal
This assumes the full bore is open (no conductors inside) — conductors occupy some volume, reducing the actual compound needed, but per NEC 501.15 and the sealing compound manufacturer's instructions, the minimum compound thickness and fill requirements must still be verified against the actual conductor fill in your specific fitting.
They open the calculator with your figures already in it
Explosion-Proof Seal-Off Compound Volume Calculator: 0.0068 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Grout volume = π × (bore radius)² × fitting length, the standard cylindrical cavity volume calculation for the sealing chamber of an explosion-proof seal-off fitting (per NEC 501.15 hazardous location sealing requirements)
Inputs used
- Fitting Bore Diameter
- 1 in
- Sealing Chamber Length
- 2 in
Confidence note: This assumes the full bore is open (no conductors inside) — conductors occupy some volume, reducing the actual compound needed, but per NEC 501.15 and the sealing compound manufacturer's instructions, the minimum compound thickness and fill requirements must still be verified against the actual conductor fill in your specific fitting.
What this calculation does not cover
- The chamber does not get filled with compound alone. A fiber dam is packed in first to hold the compound while it sets, and it occupies part of the very cavity this figure measures — so the pourable volume sits below the number above for a reason that has nothing to do with the conductors, and how far below depends on how much fiber the fitting and the conductor bundle need.
- One fitting. What actually drives the compound order on a hazardous-location job is how many seals the installation needs, and NEC 501.15 sets that by location rather than by volume: a seal within 18 in (457 mm) of each enclosure containing an arcing device, and seals where the raceway crosses out of the classified area. Take the seal count off the drawings and run this page once per fitting size.
- Sealing compound is not poured out of a tub in whatever amount a fitting needs. It comes in pre-portioned packs mixed with a fixed amount of water and it stiffens within minutes, so this volume has to be rounded up to whole packs, a part-used mix is thrown away, and one pack cannot be stretched across two fittings unless they are close enough to pour back to back.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Grout volume = π × (bore radius)² × fitting length, the standard cylindrical cavity volume calculation for the sealing chamber of an explosion-proof seal-off fitting (per NEC 501.15 hazardous location sealing requirements)
Which documents these citations point at
- National Electrical Code (NFPA 70) — 501.15 (United States)Electrical installations — conductor sizing and protection, load calculation, wiring methods, grounding and working clearances.
A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.
Cite this page
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