Check how long a storage buffer will last

Start by finding the real production rate

Run the calculation as if the storage were empty. This shows how much the machines and source materials can make each minute without help from saved inventory. Compare that number with the amount the downstream line needs.

If production matches demand, the storage is protecting the line from short interruptions and uneven arrivals. If production is lower than demand, the storage is covering a continuing shortage. It may still work, but only for a limited time.

Watch the depot during a normal run. A level that keeps falling is clear evidence that the incoming rate is too low for the current demand. If it drops during an interruption and fills again afterward, the buffer is working.

Calculate how long the stored material will last

Subtract the sustainable production rate from the demand rate. The result is the amount storage must provide each minute. Divide the usable inventory by that shortage to find the maximum run time.

For example, if a line needs 30 items/min and permanent production supplies 25, the shortage is 5 items/min. A buffer with 500 usable items can cover that difference for 100 minutes. This assumes no other machine draws from the same storage and the full 500 items are available when the run begins.

Use the inventory you can reliably count, not the maximum capacity printed on the depot. If you normally keep part of the stock for construction or another factory, remove that amount from the calculation.

1. Measure finished demand and sustainable supply in items/min.
2. Subtract supply from demand to find the shortage.
3. Record the amount of stored material that is actually available.
4. Divide usable inventory by the shortage to find the run time.
5. Compare that time with the longest job the line must finish.

Check the refill time too

A buffer only works repeatedly if production can refill it before the next burst. During idle time, the refill rate is the production that is left after any continuing demand. Divide the amount used during the burst by that refill rate.

Suppose the previous example uses all 500 stored items and the downstream line then stops completely. Production continues at 25 items/min, so the depot needs 20 minutes to replace those 500 items. If the next run starts sooner, it begins with less protection and will end sooner than the first one.

Fire Waves and transport interruptions make exact timing less predictable. Leave some margin instead of planning around a refill that finishes at the last possible minute. Check the storage before beginning an important Corporation delivery.

Use storage for a specific reason

Good reasons include smoothing short transport gaps, keeping machines supplied through an interruption, or helping a rarely used line finish a known delivery. A small shortage may be acceptable when adding another large machine would waste space and the line has plenty of time to refill.

Keep the normal production rate, intended burst rate, and expected run time with your build notes. Without that information, a full depot can make the line look sustainable when it is not.

Add another machine if the depot often runs empty, the line runs more often, or another factory starts using the same material. Run the calculation again with the new demand before relying on the buffer for another delivery.