How do you calculate days of supply?

Divide material inventory on hand by daily consumption. The result is how many production days the current stock covers before you need replenishment.

What does protected days of supply tell me?

It is the share of your supplier lead time that your current on-hand inventory and safety factor can cover, signaling how exposed you are to a delivery delay.

How much safety stock should I hold for long-lead leather?

Enough to cover the variability in both lead time and daily usage. For a 21-day lead time, many shops hold safety stock equal to several days of consumption plus a buffer for supplier slippage.

When should I place my reorder?

Place it when on-hand coverage approaches the supplier lead time. If stock covers fewer days than the lead time, you are already at risk and should order immediately.

Why does my coverage drop during peak season?

Because daily consumption rises while inventory stays flat. The same stock that covered many days at normal pace covers far fewer when the cutting line runs faster, so recalculate with peak usage.

Does this account for in-transit stock already ordered?

No. It looks only at inventory on hand. Add expected in-transit receipts manually when deciding whether to place another order.

Leather, Footwear & Accessories Manufacturing calculator

Supplier Lead Time Buffer Calculator

This calculator gauges how many days of production your current material inventory can protect against a supplier's lead time, a constant worry when tanned hides, hardware, or soling components ship on long lead times from overseas mills. Supply planners and materials managers use it to decide when to place the next purchase order and how much safety stock to hold so the cutting line never starves. It matters because footwear assembly is sequential: run out of one component and the whole line stops, idling labor and blowing delivery dates. Knowing your protected versus unprotected days turns reordering from guesswork into a scheduled decision.

What this calculator does

Calculate the required raw material buffer inventory (leather, soles, hardware, linings) to protect production against supplier lead time variability. Ensures the cutting room and assembly line do not stop due to late material deliveries.
Use this when setting safety stock levels for leather hides, outsoles, insoles, hardware, or zippers. Also useful after a supplier changes lead time, when onboarding a new tannery, or when building inventory ahead of peak season production.
It compares material inventory on hand against daily consumption to express coverage as protected and unprotected days of supply relative to lead time.

Formula used

Cycle stock = daily material consumption x supplier lead time
Required buffer inventory = cycle stock + safety stock buffer

Inputs explained

Material inventory on hand:
Daily material consumption:
Supplier safety factor:

How to use the result

Use it when timing reorders, sizing safety stock for a long-lead component, or stress-testing whether on-hand stock can survive a supplier delay.
It assumes steady daily consumption; seasonal production spikes or a sudden large order will burn through coverage faster than the figure implies.

Common questions

How do you calculate days of supply? Divide material inventory on hand by daily consumption. The result is how many production days the current stock covers before you need replenishment.
What does protected days of supply tell me? It is the share of your supplier lead time that your current on-hand inventory and safety factor can cover, signaling how exposed you are to a delivery delay.
How much safety stock should I hold for long-lead leather? Enough to cover the variability in both lead time and daily usage. For a 21-day lead time, many shops hold safety stock equal to several days of consumption plus a buffer for supplier slippage.
When should I place my reorder? Place it when on-hand coverage approaches the supplier lead time. If stock covers fewer days than the lead time, you are already at risk and should order immediately.
Why does my coverage drop during peak season? Because daily consumption rises while inventory stays flat. The same stock that covered many days at normal pace covers far fewer when the cutting line runs faster, so recalculate with peak usage.

Last reviewed 2026-05-12.