How do you calculate assembly bay utilization?

Divide the hours the bay was in use by the hours it was available. With 320 hours in use against 400 available, utilization is 320 ÷ 400 = 80%.

What is a good assembly bay utilization for a TBM erection bay?

For a single dedicated erection bay running sequential builds, sustained utilization in the 80-90% range is healthy. Above roughly 90% you have no slack for rework or a slipped delivery; below 70% the bay's capital footprint is under-earning.

Why is my utilization below target?

In this example utilization is 80% against an 85% target, a 5-point gap. On TBM builds the usual culprits are crane contention with an adjacent bay, late long-lead components (main bearing, cutterhead drives), and staging space clogged with segments or backup gantry.

Does utilization include shift patterns and holidays?

Only through the 'hours available' figure. If you run one shift, count one shift of hours as available; if the bay is theoretically open around the clock but you never staff nights, decide deliberately whether those hours are truly available or you will understate utilization.

Utilization vs occupancy — what's the difference?

Occupancy just means a machine is physically parked in the bay. Utilization as computed here treats occupied hours as 'in use', so a machine sitting idle awaiting parts still counts. Track a separate work-content or earned-hours metric to expose that hidden idle time.

Should I aim for 100% bay utilization?

No. On sequential heavy builds you need buffer for teardown, cleaning, rework, and delivery slip. Chasing 100% removes all recovery room and usually just pushes delays downstream into the tunnel launch schedule.

Tunnel Boring & Heavy Civil Equipment calculator

Assembly Bay Utilization Calculator

Assembly bay utilization measures how much of a TBM assembly bay's available time was actually spent building or refurbishing machines, expressed as a percentage. Heavy-civil OEMs and TBM refurb yards track it because a single erection bay large enough to stand up a 10 m diameter shield is one of the most capital-intensive footprints on the site. Fabrication managers and project schedulers use bay utilization to decide whether a second bay is justified, whether a factory-acceptance build is slipping, and where crane and staging conflicts are stealing productive time. Because TBM assembly runs in long, sequential campaigns rather than repeating cycles, even a few points of idle bay time can translate into weeks of schedule risk on a tunnel drive.

What this calculator does

Measure assembly bay utilization for Tunnel Boring & Heavy Civil Equipment — hours in use as a percentage of hours available.
Use it to judge whether the assembly bay in Tunnel Boring & Heavy Civil Equipment is a bottleneck or has spare capacity.
It divides the hours a bay was actively occupied by build work by the total hours it was available, then compares the result to your target.

Formula used

Utilization = hours in use ÷ hours available
Gap to target = target utilization − utilization

Inputs explained

Hours the assembly bay was in use:
Hours the assembly bay was available:
Target utilization:

How to use the result

Use it at the end of a build campaign or on a rolling weekly basis to see whether a bay is earning its footprint before committing capital to a second erection bay.
Occupancy is not the same as productive work — a bay can show 80% utilization while a machine sits parked waiting on a late gearbox, so pair this with an actual work-content metric before drawing conclusions.

Current U.S. benchmarks

As of May 2026, U.S. manufacturing runs at 75.6% of capacity (Federal Reserve via FRED), up 0.2 points from a year earlier. Enter your own plant's utilization; the national figure is a reference point for how loaded the industry is.
Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate assembly bay utilization? Divide the hours the bay was in use by the hours it was available. With 320 hours in use against 400 available, utilization is 320 ÷ 400 = 80%.
What is a good assembly bay utilization for a TBM erection bay? For a single dedicated erection bay running sequential builds, sustained utilization in the 80-90% range is healthy. Above roughly 90% you have no slack for rework or a slipped delivery; below 70% the bay's capital footprint is under-earning.
Why is my utilization below target? In this example utilization is 80% against an 85% target, a 5-point gap. On TBM builds the usual culprits are crane contention with an adjacent bay, late long-lead components (main bearing, cutterhead drives), and staging space clogged with segments or backup gantry.
Does utilization include shift patterns and holidays? Only through the 'hours available' figure. If you run one shift, count one shift of hours as available; if the bay is theoretically open around the clock but you never staff nights, decide deliberately whether those hours are truly available or you will understate utilization.
Utilization vs occupancy — what's the difference? Occupancy just means a machine is physically parked in the bay. Utilization as computed here treats occupied hours as 'in use', so a machine sitting idle awaiting parts still counts. Track a separate work-content or earned-hours metric to expose that hidden idle time.

Last reviewed 2026-05-12.