Maintenance Float Calculator
Equipment float sizing from readiness rate and repair time.
About this calculator
This calculator sizes an equipment float -- spare items held in reserve to backfill equipment currently in maintenance -- from fleet size, target readiness, repair time, and failure rate. Float required is the number of items expected to be in maintenance at any moment, rounded up (line 16), and total equipment, average repair days, and monthly failure rate all move that figure by an identical proportional amount since they multiply together in the same formula (line 10) -- doubling any one of the three doubles the in-maintenance count and, with it, the float required. Target OR rate does not affect Float required or Avg in maintenance at all (line 10 has no operationalReadiness term) -- it only appears in Deficit From Target, where it dominates every other input by a wide margin (line 15): moving the target from 90% down to 50% swings the deficit far more than any realistic change to fleet size, repair time, or failure rate.
Achieved OR (%) is a fixed 100% for every combination of inputs the calculator accepts, because Float required is defined as exactly enough spare items to replace whatever is currently down (line 16), and adding that many items back to the pool always restores the fleet to its full authorized count (lines 19-20) -- by construction, a correctly sized float always shows 100% achieved readiness, regardless of what target OR rate was entered. Deficit From Target is the figure that actually reflects the target: it is the gap between authorized strength and the target rate before any float is added (line 15).
Safety Notice
This calculator provides estimates only. Always follow manufacturer guidelines, industry standards, and applicable safety codes. Incorrect application of these calculations could result in injury or property damage. When in doubt, consult a qualified professional.
Inputs
Results
Float required
5
How to Use This Calculator
- Enter the total equipment count in the fleet.
- Set the target operational readiness (OR) rate (%) — typically 90% for combat units; this input only affects Deficit From Target, not Float required or Achieved OR (%).
- Input average repair time (days) and monthly failure rate as a fraction (e.g., 0.10 = 10% of fleet fails per month) — these two and total equipment carry equal weight in sizing Float required.
- Review Float required — the number of spare equipment items needed in the float pool.
- Achieved OR (%) always shows 100% once a correctly sized float is in place, by design; use Deficit From Target instead to see the shortfall the float is closing, and Monthly repairs for maintenance staffing.
How the result changes with Total equipment
| Total equipment | Float required |
|---|---|
| 50 | 3 |
| 75 | 4 |
| 150 | 7 |
| 250 | 12 |
What each input means
- Total equipment
- Total equipment items in the fleet.
- Target OR rate (%)
- Target operational readiness rate.
- Avg repair time (days)
- Average days to complete a repair.
- Monthly failure rate
- Fraction of equipment failing per month.
What each result means
- Float required
- Spare equipment items needed as float.
- Avg in maintenance
- Average items in maintenance at any time.
- Achieved OR (%)
- Operational readiness with float.
- Monthly repairs
- Expected repair actions per month.
- Monthly parts demand
- Estimated repair parts needed per month.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTotal equipment = 100, Target OR rate (%) = 90, Avg repair time (days) = 14, Monthly failure rate = 0.1 = 4 input(s) provided
- Calculate Float requiredFloat required = ceil(inMaintenanceCount)5 = 5
- Calculate Avg in maintenanceAvg in maintenance = round(inMaintenanceCount * 100) / 1004.67 = 4.67
- Calculate Achieved ORAchieved OR = round((min(totalEquipment, availableWithFloat) / totalEquipment) * 10000) / 100100 = 100
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does Achieved OR (%) always show 100%, no matter what I enter?
By construction. Float required is defined as exactly enough spare items to cover whatever is currently in maintenance, rounded up (line 16), and adding that float back to the available pool always restores the fleet to its full authorized count (lines 19-20) -- so a correctly sized float mathematically produces 100% achieved readiness for every combination of inputs, including every value of Target OR rate. This is not a bug: it reflects the real-world purpose of a maintenance float, which is to keep the using unit at authorized strength despite items being down for repair.
If Achieved OR never changes, what tells me whether my target is realistic?
Deficit From Target. It measures the gap between total equipment and the target OR rate before any float is added (line 15), and Target OR rate dominates every other input in this specific calculation -- moving the target from 90% down to 50% swings the deficit far more than any realistic change to fleet size, repair time, or failure rate. Use it to see how large a gap the float you calculate is actually closing.
Do total equipment, repair time, and failure rate matter equally for Float required?
Yes. Float required rounds up the expected in-maintenance count, which is total equipment times average repair days divided by 30 times monthly failure rate, all multiplied together (line 10) -- a given percentage increase to any one of the three raises the in-maintenance count, and Float required with it, by the same percentage. None of the three takes priority over the others in this formula.
Does Target OR rate change how many spare items I need to buy?
No. Float required is computed purely from total equipment, average repair days, and monthly failure rate (line 10); Target OR rate never enters that formula. It only affects Deficit From Target, the separate figure showing how far short of the target the fleet sits before any float is purchased.
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