Ask ten maintenance managers what “good” wrench time looks like and you’ll get ten answers, most of them wrong in the optimistic direction.
The figure that gets repeated most is 25 to 35 percent for a typical site and about 55 percent for world-class. Dig into the primary sources and it’s a bit messier: Palmer’s open writing points to roughly 35 percent typical, and Smith and Mobley put most companies at 18 to 30 percent. The 55 percent world-class mark is Palmer’s best-practice benchmark.
That gap is a real pool of recoverable labor, and tapping it doesn’t cost a single new hire.
What wrench time measures, and where the numbers come from
Wrench time is the share of a technician’s available shift spent making productive progress on a job. The narrowest reading counts only hands-on tool time. Palmer’s reading is broader: any activity that moves the job forward, which can take in troubleshooting, lockout/tagout, and job-site paperwork. Both readings strip out the big time sinks, travel, waiting for parts, hunting for tools, and breaks. The line between the two readings is exactly where definitions drift, which we cover below.
Wrench time is a recognized best-practice metric. SMRP lists it as Metric 5.6.1 in its Best Practices metrics set, which gives practitioners a common reference point. That recognition doesn’t settle the definition, though. The detailed SMRP definition, and any best-in-class target, sit in the members-only document, and field teams still draw the productive line in different places.
The numeric targets are a different story. No published ISO or EN standard sets a “world-class” wrench time figure. The typical and best-practice numbers come from practitioner literature, chiefly Doc Palmer and the team of Ricky Smith and R. Keith Mobley, both writing from decades of plant-floor work sampling. That distinction matters for how confident you should be, so we built it into the table.
The Reliable Confidence Score
| Claim or Source | Figure | Reliable Confidence | What It Really Means |
|---|---|---|---|
| Claim or SourceTypical wrench time, most industrial sites (Palmer; Smith & Mobley) | Figure~35% | Reliable ConfidenceMediumPalmer’s open figure is 35%; the wider band is consensus | What It Really MeansPalmer’s accessible writing puts a typical good plant near 35%. The broader 25 to 35% band is widely repeated but harder to pin to an open primary source. Smith & Mobley put most companies at 18 to 30%, though that figure sits in their paid book. |
| Claim or Source“Good,” with a working planning and scheduling program | Figure~45% | Reliable ConfidenceMediumWidely cited milestone, softer sourcing | What It Really MeansOften quoted as the halfway mark. Palmer’s model tends to jump from roughly 35% to roughly 55%, so treat 45% as a waypoint, not a hard standard. |
| Claim or SourceWorld-class / best practice (Palmer) | Figure~55% | Reliable ConfidenceHighPalmer’s benchmark, stated as achievable | What It Really MeansPalmer calls 55% best practice and sustainable, and warns that 80% is a fantasy. It’s widely used as the world-class label, but it’s Palmer’s benchmark, not a codified cross-industry standard. |
| Claim or SourceCapacity gain, 35% to 55% (Palmer) | Figure+57% | Reliable ConfidenceHighArithmetic; theoretical capacity only | What It Really Means55 ÷ 35 = 1.57. A 30-person crew gains the capacity of 47. It’s a ratio, so real output still depends on backlog, scheduling discipline, parts, and staffing. |
| Claim or Source“World-class equals 65% or higher” as a fixed target | Figure60%+ | Reliable ConfidenceLowRarely credible or sustained | What It Really MeansThe 55 to 65% upper band (Smith & Mobley) gets quoted as if 65% were routine, but the top of it is a reach for most plants, especially where lockout, permits, or remote access slow every job. |
| Claim or SourceSMRP best-in-class target (Metric 5.6.1, Wrench Time) | FigureNot public | Reliable ConfidenceMediumMetric exists; target not in open material | What It Really MeansSMRP lists Wrench Time as Metric 5.6.1 (Pillar 5, Work Management). Its detailed definition, and any best-in-class target, sit in the paid Best Practices document, so treat any quoted SMRP number as commonly cited, not verified here. |
The Big Takeaway
Here’s where the real money is: the math on closing the gap.
Doc Palmer’s point is that the jump from typical to world-class looks small and pays huge. Moving a crew from 35 to 55 percent wrench time is a 57 percent gain in capacity (55 ÷ 35 = 1.57). In Palmer’s model, those recovered hours flow to proactive work, since the crew was already sized to cover the reactive load.
Going from 35 to 55 percent wrench time turns a 30-person crew into the equivalent of 47 people, with nobody new on the payroll. That is the whole business case for planning and scheduling in one ratio.
That 57 percent is theoretical capacity, not an automatic result. Turning it into real output still needs the backlog, parts, supervision, and equipment access to fill the recovered hours, and some of that capacity gets absorbed by corrective or emergent work. The leverage is real because the cost is fixed: you’re paying for the full shift either way, and wrench time tells you how much of it reaches the equipment.
Why the numbers vary
The same plant can post very different wrench time numbers depending on how you measure it.
Study design drives most of the spread. A one-day snapshot during a turnaround week says nothing about normal operations. A rolling work sampling study across several weeks gives a stable number. The two can differ by a wide margin.
Observation changes behavior. Crews who feel watched look busier, and technicians who suspect a headcount cut is coming will look very busy during the study window. That alone can inflate a result.
Definition drift is the quiet one. If one plant counts “walking to the storeroom” as productive and another counts it as travel, their numbers aren’t comparable even when both call the metric “wrench time.” This is why the SMRP 5.6.1 definition matters more than the benchmark.
Plant type sets the ceiling. A heavy process environment with vessel entry, lockout/tagout, and remote equipment access has less room to run than a general manufacturing line, because access and permitting eat into every job. The same planning program will land at different numbers in those two settings.
How to use the benchmark safely
Compare yourself to yourself. Run a consistent work sampling study, fix your top three time-wasters, then re-measure in 90 days. Your own trend line is worth more than another plant’s number measured under different rules.
Pair it with context. Wrench time read alone is misleading. Read it next to schedule compliance, backlog, and planned work percentage, and the picture of whether work management is leaking hours gets clear.
Set a realistic target. A team starting low can often book a meaningful gain in the first improvement cycle, then build from there. A sustained move to best-practice levels is a long-term program built on consistent planning and scheduling.
Where teams go wrong
They chase 65 percent. The defensible anchor is 55 percent. Before trusting a number above 60 percent, check how the plant defines and measures wrench time, because small differences there can swing the result.
They weaponize the metric. Palmer’s own caution is blunt: you don’t have to measure wrench time, and if you turn it into a surveillance tool, the data becomes useless and the crews stop trusting you. Use it to find process leaks, not to justify cuts.
They confuse it with other metrics. Wrench time, utilization, and Mean Time to Repair measure different things, and each gets defined differently from shop to shop. Wrench time tracks the productive share of a shift; MTTR tracks how long a repair takes. Treating them as interchangeable, or assuming everyone draws the lines the same way, produces nonsense benchmarks.
Methodology
We pulled the figures from primary practitioner sources and the standards framework, then rated each one on the Reliable Confidence Score.
Palmer’s open writing supports a typical figure near 35 percent and a 55 percent best practice, so those anchors carry the most weight. The wider 25 to 35 percent band, and the Smith and Mobley ranges (18 to 30 percent for most companies, 55 to 65 percent at the top), come from the paid literature, including Smith and Mobley’s Rules of Thumb for Maintenance and Reliability Engineers (Butterworth-Heinemann, 2007), so we rated those Medium. The 57 percent figure is Palmer’s arithmetic (55 ÷ 35), which we treat as theoretical capacity rather than a measured field outcome.
One honest caveat sits behind two of the Medium ratings. No published ISO or EN standard sets a numeric wrench time target. The world-class numbers are practitioner consensus, and SMRP’s own best-in-class figure for Metric 5.6.1 lives behind its members-only Best Practices document, so we could not verify the exact value in open material.
Bottom Line
The figure everyone repeats is 25 to 35 percent typical. The primary sources are lower and narrower: about 35 percent from Palmer, 18 to 30 percent from Smith and Mobley. Best practice, the level most people call world-class, is about 55 percent. The prize for closing that gap, in Palmer’s model, is a 57 percent gain in capacity, headroom that turns into proactive work when the backlog and parts are there to fill it.
Measure it carefully with a real work sampling study, or follow Palmer’s advice and don’t measure it at all. A bad wrench time number does more damage than no number.
Sources
- Doc Palmer, Maintenance Planning and Scheduling Handbook, McGraw-Hill. https://books.google.com/books/about/Maintenance_Planning_and_Scheduling_Hand.html?id=CT5zaQC0uKAC
- Doc Palmer, “Plan-it fitness: the great value of maintenance planning,” Plant Services (Palmer’s Planning Corner). https://www.plantservices.com/planned-maintenance/planning-and-scheduling/article/11303144/plan-it-fitness-the-great-value-of-maintenance-planning
- Doc Palmer, “Understanding the math of maintenance planning and scheduling,” Plant Services. https://www.plantservices.com/planned-maintenance/planning-and-scheduling/article/11295301/understanding-the-math-of-maintenance-planning-and-scheduling
- Ricky Smith and R. Keith Mobley, Rules of Thumb for Maintenance and Reliability Engineers, Butterworth-Heinemann/Elsevier, 2007 (ISBN 9780750678629). https://shop.elsevier.com/books/rules-of-thumb-for-maintenance-and-reliability-engineers/smith/978-0-7506-7862-9
- SMRP, Best Practices, Metrics and Guidelines (the metrics set that includes Wrench Time). https://smrp.org/Learning-Resources/SMRP-Library/Best-Practices-Metrics-Guidelines
- SMRP Best Practices Metrics Workshop (lists Wrench Time as Metric 5.6.1 under Pillar 5, Work Management), hosted by PEMAC. https://pemac.org/sites/default/files/2018_SMRP_BPMW_Full_Day.pdf
