Free tool
Order quantity calculator: how much inventory to order
Estimate the next order after allowing for demand while stock arrives, time until the next review, your buffer and stock already available.
Your demand and stock
Use the same daily unit basis throughout. A blank or 0 supplier minimum means none; a blank or 0 case pack means individual units.
How much inventory to order
336 units
- Target stock including buffer
- 526 units
- Need before pack and minimum
- 326 units
- Case pack rounding
- 10 units
The supplier minimum applies only when an order is needed. The quantity is then rounded up to a whole case pack.
The formula
Target stock = daily demand × (lead time + review period) + safety stock
Need = max(0, target stock − on hand − on order)
If need > 0, raise to supplier minimum, then round up to a whole case pack
- Review period
- Days until you check the item and can order again.
- Safety stock
- Extra units held for uncertainty in demand or delivery.
- On order
- Units already purchased and expected to arrive in time.
Worked example
- At 20 units/day, 14 lead-time days and 7 review days, demand to cover is 20 × (14 + 7) = 420 units.
- Add 106 safety-stock units for a target of 420 + 106 = 526 units.
- Subtract 150 on hand and 50 already on order: need is 526 − 150 − 50 = 326 units.
- That already meets the 100-unit supplier minimum. Round 326 up to whole 24-unit cases: order 336 units.
When it applies
- Periodic ordering with a known lead time, review cycle and target buffer.
When it breaks down
- A flat demand average misses seasonal or promotional spikes.
- If on-order stock will arrive too late, it cannot safely cover this target.
Common mistakes
Ignoring open orders
Stock already on its way reduces how much you need to buy again.
Leaving out review time
The next order may not be placed until the following review, so stock must cover that interval too.
Rounding before the minimum
Apply the supplier minimum to a positive need, then round to the case pack.
Questions
How do I calculate how much inventory to order?
Cover forecast demand through lead time and the next review, add safety stock, subtract on hand and timely on-order units, then apply supplier pack and minimum rules.
Why include a review period?
It covers demand until the next opportunity to place another order.
Does the supplier minimum force an order when stock is sufficient?
No. A minimum applies only after the unrounded calculation shows a positive need.
Is order quantity the same as reorder point?
No. Reorder point is a trigger; this calculation estimates units for the next order.
How do case packs affect order quantity?
The positive quantity is rounded up to a whole number of cases.
Related
Published by Skuvelo. Results are estimates computed from the figures you enter, not a reading of your own sales or stock.
A calculator answers once. Skuvelo keeps answering.
This tool computes one number from what you type. Skuvelo computes it continuously, for every SKU, from your own sales and stock.