How do you calculate OT asset inventory coverage?

Divide inventoried assets by expected assets in scope and multiply by 100. With 820 of 930 assets inventoried, coverage is 88.17%, leaving a 9.83-point gap to a 98% target.

What is a good OT asset inventory coverage?

Mature programs target 95% or higher, with many setting 98% to 100% for safety-critical zones. The example's 88.17% is a solid working baseline but still short of the 98% target by nearly 10 points.

Why is asset inventory the first OT security control?

Every other control — patching, segmentation, monitoring, vulnerability management — depends on knowing the asset exists. An uninventoried PLC can't be patched, watched, or protected, so coverage gates the whole program.

How do I find the 'expected assets in scope' number?

Reconcile engineering drawings, P&IDs, network scans, purchase records, and walk-downs. The closer this denominator reflects reality, the more trustworthy your coverage percentage.

What does the coverage gap tell me?

The gap is the distance from current coverage to your target. Here it's 9.83 points, meaning roughly that share of expected assets still needs to be discovered and added before you hit 98%.

Can coverage be over 100%?

If your inventory exceeds the expected count, you've likely under-estimated scope or double-counted assets. Treat above-100% as a signal to recheck both the inventory and the expected total.

Industrial Cybersecurity & OT Risk calculator

OT Asset Inventory Coverage Calculator

OT Asset Inventory Coverage measures what fraction of your expected industrial control-system assets — PLCs, RTUs, HMIs, drives, switches, and engineering workstations — are actually accounted for in your asset inventory. You cannot secure or patch what you cannot see, so coverage is the foundational metric of any OT security program and the first thing ISA/IEC 62443 and CIS Controls assessors ask about. OT security leads and plant IT use it to track discovery progress, expose blind spots, and report against a coverage target to leadership. The companion gap figure tells you exactly how many percentage points of work remain.

What this calculator does

Calculate OT asset inventory coverage using discovered assets, expected assets, and target coverage.
Use it when measuring asset visibility for PLCs, HMIs, SCADA nodes, network devices, servers, and engineering workstations.
It divides inventoried OT assets by the expected total to give a coverage percentage, then compares that to your target.

Formula used

OT asset inventory coverage = OT assets inventoried ÷ expected OT assets in scope × 100
OT asset inventory coverage gap to target = OT asset inventory coverage - target asset inventory coverage

Inputs explained

OT assets inventoried:
Expected OT assets in scope:
Target asset inventory coverage:

How to use the result

Use it to track asset-discovery progress and report inventory completeness against a program target or audit requirement.
It depends entirely on a credible 'expected assets in scope' figure — if that denominator is wrong, your coverage percentage is misleading even at 100%.

Common questions

How do you calculate OT asset inventory coverage? Divide inventoried assets by expected assets in scope and multiply by 100. With 820 of 930 assets inventoried, coverage is 88.17%, leaving a 9.83-point gap to a 98% target.
What is a good OT asset inventory coverage? Mature programs target 95% or higher, with many setting 98% to 100% for safety-critical zones. The example's 88.17% is a solid working baseline but still short of the 98% target by nearly 10 points.
Why is asset inventory the first OT security control? Every other control — patching, segmentation, monitoring, vulnerability management — depends on knowing the asset exists. An uninventoried PLC can't be patched, watched, or protected, so coverage gates the whole program.
How do I find the 'expected assets in scope' number? Reconcile engineering drawings, P&IDs, network scans, purchase records, and walk-downs. The closer this denominator reflects reality, the more trustworthy your coverage percentage.
What does the coverage gap tell me? The gap is the distance from current coverage to your target. Here it's 9.83 points, meaning roughly that share of expected assets still needs to be discovered and added before you hit 98%.

Last reviewed 2026-05-12.