Purchasing & cost

Purchase Order Quantity Calculator

Focus on the order quantity needed to reach target coverage after a new purchase order arrives.

Calculations run locally in your browser.

Worked example

Example scenario: from raw need to an orderable quantity

The numbers below are illustrative data for one product. They are not real customer data.

Inputs: on-hand inventory 220 units; no inbound; average daily sales 12 units; supplier lead time 14 days; safety stock 50 units; target coverage 20 days; MOQ 0; case pack 48 units; unit cost $6.00.
Projected inventory at PO arrival: 220 − (12 × 14) = 52 units, with no inbound included.
Target level: 50 + (12 × 20) = 290 units.
Raw order need: 290 − 52 = 238 units.
MOQ: 0, so no minimum applies.
Case pack: 48 — 238 rounds up to 240 units (5 full cases).
Estimated purchase cost: 240 × $6.00 = $1,440.00.

What this result means

The final order quantity can be higher than the raw requirement for two reasons: a MOQ floor when raw need is small, and case-pack or order-multiple rounding, because suppliers ship whole cases. Confirmed inbound is only included in projected inventory when it becomes sellable before the new purchase order arrives; inbound that arrives later is excluded. The result is an orderable planning estimate, not an approved purchase decision.

Review before acting

Confirm the raw need covers your real coverage target before accepting a rounded quantity.
Check whether the rounded quantity fits cash, storage, and shelf life.
Confirm MOQ, case pack, and unit cost against the current supplier terms.
Confirm inbound timing assumptions match reality for this purchase.

Input guide

On-hand inventory: units — sellable stock right now.
Confirmed inbound quantity: units — optional; blank means zero.
Expected arrival in days: days — required only when inbound is greater than zero; included only if it arrives before the new PO.
Average daily sales: units per day.
Supplier lead time: days — until the new PO becomes sellable.
Safety stock: units — held above the coverage target.
Target coverage: days of demand the stock level should reach.
MOQ: units — minimum the supplier accepts; 0 means none.
Case-pack / order multiple: units — orders round up to this; 0 means none.
Unit cost: currency per unit; blank leaves the cost estimate unavailable.

What this tool estimates

When to use this tool: Use this tool when you know your coverage target and supplier ordering rules, and need the actual orderable quantity and its estimated cost.

It estimates a net purchase quantity from projected inventory at the new PO arrival, your safety stock, and a target coverage period. The raw need is the non-negative difference between that target stock level and projected inventory at arrival. Confirmed inbound is included only when it arrives by the new PO arrival date; MOQ and case-pack rules are applied afterward.

Inputs to verify

Use sellable on-hand stock, confirmed receipt timing, a lead time through sellable availability, and a target coverage period that reflects your own planning policy.

Supplier rules

MOQ is applied after raw need when an order is needed, then the final quantity rounds up to a complete case pack.

Important assumptions

Target coverage, MOQ, and case packs are business constraints, not forecasts. The estimated purchase cost uses only the unit landed cost you enter and is not a cash-flow model.

When not to rely on the result alone

Before placing a PO, review cash availability, storage capacity, shelf life, product obsolescence, supplier capacity, payment terms, confirmed inbound status, and purchasing approval conditions.

Check stockout timing, check reorder point, or read the planning basics.

FAQ

Purchase quantity questions

Why can the final quantity exceed the raw need?

MOQ and case-pack rules are applied after the raw calculation, which can increase the final order size.

When is inbound included in projected inventory?

Only when its arrival date is on or before the new purchase order arrival date.