How many duct spacers do I need per 100 ft?

At a 5 ft interval, a 100 ft run needs about 21 spacer sets (100 ÷ 5 = 20, plus one at the start). At a 10 ft interval it needs about 11. The interval that governs your job is the one on the project engineering drawings, so always defer to the specification.

How far apart should duct spacers be placed?

A common field practice is a spacer set every 5 to 10 feet and at every coupling, which keeps the bank aligned during the concrete pour or backfill. Tighter intervals give more support; the project drawings set the interval that applies.

Does the spacer count depend on the number of conduits?

The count of spacer sets along a run depends on run length and interval, not conduit count — a single base-and-intermediate set holds a full cross-section of conduit. A wider or taller duct bank uses larger or additional spacers per set, not more sets along the length.

Underground Electrical

How Many Duct Spacers Per 100 ft?

How to estimate duct spacer quantity for a conduit duct bank — spacer sets per 100 ft at 5–10 ft intervals, with a free calculator. Confirm against your project specification.

By Innovative Plastics Manufacturing Published July 14, 2026

Estimating how many duct spacers a run needs comes down to two numbers: the length of the run and how often a spacer set repeats along it. This guide gives the simple formula, a calculator to run your own numbers, and the field practice behind the interval — then points you to the duct spacers that hold the bank together.

The quick answer

For a single 100 ft run, the number of spacer sets is the run length divided by the spacer interval, plus one set at the start:

At 5 ft intervals: 100 ÷ 5 = 20, +1 = about 21 sets
At 8 ft intervals: 100 ÷ 8 = 13 (rounded up), +1 = about 14 sets
At 10 ft intervals: 100 ÷ 10 = 10, +1 = about 11 sets

Multiply by the number of parallel runs in the duct bank, then round up to full cases. Remember that a single base and intermediate spacer set holds an entire cross-section of conduit — so more conduits in the bank means larger or additional spacers per set, not more sets along the length.

Estimate your run

Calculator

Duct spacer quantity estimator

Enter the run length and the spacer interval from your drawings. The estimate assumes a set at each interval plus one at the start of the run. Confirm against your project specification before ordering.

Run length (ft) Spacer interval (ft) Number of runs

Estimated spacer sets: 21 (1 run × 100 ft at 5 ft intervals)

The calculator uses the same formula shown above: one set per interval along the run, plus one at the start. It is an estimate to help you plan and order — the governing quantity is always the one your project specification and applicable code require.

Why the interval matters

Duct spacers exist to hold conduit on a fixed grid so that concrete or backfill flows around every duct and the bank cures straight, without drifting or floating during the pour. Placing a set often enough keeps the conduit from sagging between supports, especially at couplings where the duct is most flexible. That is why a spacer set at every coupling is common practice in addition to the running interval.

A tighter interval (every 5 ft) gives more support and a stiffer, more registered bank; a looser interval (every 10 ft) uses fewer parts on straight, well-supported runs. Neither is a universal rule — the interval that governs your job is the one on the project engineering drawings. Our guide to duct bank spacing covers the related questions of conduit separation and concrete cover.

Base, intermediate, and clip spacers

How you count depends a little on the spacer type:

Base and intermediate spacers build stacked, multi-row duct banks. A “set” is the base course plus the intermediate spacers that stack the rows above it; you place a set at each interval along the run.
Clip spacers are lighter, single-tier snap-on spacers for 1”–2” runs. They clip directly onto the conduit at each interval rather than building up from a base.

Once you have a quantity, order by the case — case quantities are listed on each product page. Pre-assembly is available; just ask. And always confirm spacer intervals against your project specification and the applicable code before you build.

Frequently asked questions

How many duct spacers do I need per 100 ft?: At a 5 ft interval, a 100 ft run needs about 21 spacer sets (100 ÷ 5 = 20, plus one at the start). At a 10 ft interval it needs about 11. The interval that governs your job is the one on the project engineering drawings, so always defer to the specification.
How far apart should duct spacers be placed?: A common field practice is a spacer set every 5 to 10 feet and at every coupling, which keeps the bank aligned during the concrete pour or backfill. Tighter intervals give more support; the project drawings set the interval that applies.
Does the spacer count depend on the number of conduits?: The count of spacer sets along a run depends on run length and interval, not conduit count — a single base-and-intermediate set holds a full cross-section of conduit. A wider or taller duct bank uses larger or additional spacers per set, not more sets along the length.