OEE Calculator

What this tool does

CM8-04 calculates Overall Equipment Effectiveness (OEE) for a single machine or production line over one shift or run. Enter the shift time, planned stops, unplanned downtime events, ideal cycle time and piece counts; the tool computes Availability, Performance, Quality and OEE, maps every lost minute into the classic six big losses, and lets you log runs to track the trend over time.

Everything runs inside this single HTML file. No installation, no account, no network requests — your production data never leaves your computer.

What is OEE, in plain terms?

OEE answers one question: “Of the time we planned to run this machine, what fraction actually produced good parts at the ideal rate?” It multiplies three independent ratios:

A machine that ran 90% of its planned time, at 90% of its ideal speed, making 90% good parts has an OEE of 0.9 × 0.9 × 0.9 = 72.9% — losses compound, which is exactly why OEE is a tougher, more honest number than any of its parts alone.

An OEE of 100% means: making only good parts (100% Quality), as fast as possible (100% Performance), with no unplanned stops (100% Availability).

The three factors

Availability — did it run when planned?

Breaks, lunches, planned maintenance and no-demand time are excluded from OEE — they are a scheduling decision, not an equipment loss. Unplanned downtime (breakdowns, changeovers, waiting for material or operators) is what Availability punishes.

Performance — did it run at full speed?

Performance captures speed losses: minor stops too short to record (jams, sensor blocks, feed hiccups) and running below the ideal rate. The ideal cycle time is the fastest time per piece the process can repeatably achieve — the design or rated speed, not the average of recent history.

Quality — were the parts good?

Count as defects every piece that did not come out right the first time — scrap and rework. A reworked part may be saleable, but the machine time it consumed was not fully productive (“first pass yield” thinking).

What the numbers mean

• OEE — Rating in this tool — Interpretation
• ≥ 85 % — World class — Long-standing benchmark for discrete manufacturing (≈ 90% A × 95% P × 99% Q).
• 60–85 % — Typical — Common for reasonably-run operations; solid improvement potential remains.
• 40–60 % — Fair — Substantial losses; the six-big-losses table will show where.
• < 40 % — Low — Not unusual for unmeasured processes — measuring is the first improvement.

The six big losses

• # — Loss — OEE factor — In this tool
• 1 — Equipment failure — Availability — Downtime events tagged “Breakdown”.
• 2 — Setup & adjustments — Availability — Downtime events tagged “Changeover / setup”. Material-wait, operator and other stops are grouped alongside as availability losses.
• 3 — Idling & minor stops — Performance — Computed together as speed loss: run time minus (ideal cycle × total count). Separating 3 from 4 needs machine-level data collection.
• 4 — Reduced speed — Performance
• 5 — Startup / yield losses — Quality — Computed together as ideal cycle × defect count — the machine time invested in bad pieces.
• 6 — Production defects — Quality

Entering good data

• Shift length — the full scheduled window (480 min for 8 h, 720 for 12 h).
• Breaks & planned stops — everything you deliberately did not run: lunches, breaks, planned PM, meetings, no scheduled demand.
• Downtime events — record each unplanned stop with a reason category. Categories drive the six-big-losses table and the CSV columns, so tag consistently.
• Ideal cycle time — use the rated/design speed. If Performance shows over 100%, the tool flags it: your “ideal” is set slower than reality, which quietly hides speed losses.
• Counts — total includes every piece started; defects include rework.

Worked example

Saving your work

• Autosave: the current run and the run log are kept in this browser's local storage automatically (see the “Autosaved” indicator in the toolbar) and restored next time you open the file.
• Save: writes the whole project to this browser immediately and flashes “Saved ✓” with the time. Use it before closing if you want to be certain; it stores nothing outside your own browser.
• Save project (.json): saves the complete state — current inputs, downtime events and the full run log — as a local file you can archive or move to another computer.
• Export CSV: a spreadsheet-ready run log including per-category downtime minutes.
• Print report: builds a formatted report — summary tiles, all five charts, the loss breakdown, the run log and your closing notes — and opens the browser print dialog (save as PDF works too). The report is rebuilt from current data every time, including when you print with Ctrl+P. Fill in “Report header” on the Calculator tab to title it.
• Reset: a two-step button — press once to arm, again to confirm. It erases the inputs, the run log, the report header and everything this tool has saved in your browser, returning it to a clean first run. Export a project file first if you want a copy.