Calculator Inputs
Use item quantities as weights. Add adjustments, discounts, handling, insurance, and tax to produce a final weighted average cost per unit.
Example Data Table
| Item | Quantity | Unit Cost | Extended Cost |
|---|---|---|---|
| Batch A | 120 | 14.50 | 1,740.00 |
| Batch B | 80 | 16.20 | 1,296.00 |
| Batch C | 150 | 13.80 | 2,070.00 |
| Batch D | 60 | 17.10 | 1,026.00 |
Example base weighted average = (1740 + 1296 + 2070 + 1026) ÷ (120 + 80 + 150 + 60) = 14.9561 per unit before adjustments.
Formula Used
Base Cost Total = Σ(Quantity × Unit Cost)
Base Weighted Average = Σ(Quantity × Unit Cost) ÷ Σ(Quantity)
Net Subtotal = Base Cost Total + Additional Costs + Handling + Insurance − Discount
Tax Amount = Net Subtotal × Tax Rate
Final Weighted Average Cost = (Net Subtotal + Tax Amount) ÷ Total Quantity
Weighted Variance = Σ[Quantity × (Unit Cost − Base Weighted Average)²] ÷ Σ(Quantity)
Weighted Standard Deviation = √Weighted Variance
How to Use This Calculator
- Enter one or more item labels, quantities, and unit costs.
- Add optional overhead, handling, insurance, discount, and tax values.
- Press the calculate button to place results under the header.
- Review total cost, weighted average, spread, and cumulative behavior.
- Use the CSV or PDF buttons to export the summary.
- Use the graph to compare extended cost and running average.
Frequently Asked Questions
1) What does weighted average cost mean?
It is the average unit cost after weighting each price by its quantity. Larger quantities influence the result more than smaller ones.
2) Why is this better than a simple average?
A simple average treats every price equally. Weighted average cost respects the fact that one batch may contain far more units than another.
3) Can I include overhead and fees?
Yes. Additional costs, handling, insurance, discounts, and tax are included so the final unit cost reflects more realistic operational spending.
4) What does weighted standard deviation show?
It measures how widely the unit costs are spread around the weighted mean. A higher value suggests more cost inconsistency across batches.
5) Does item order change the final answer?
No. The final weighted average stays the same regardless of order. The cumulative graph changes visually because it tracks the running average sequence.
6) Can this be used for inventory analysis?
Yes. It works well for inventory costing, purchasing analysis, batch valuation, procurement reviews, and general quantity-weighted pricing studies.
7) What happens if I enter a zero quantity?
Rows with zero or missing quantity are considered invalid for calculation because they cannot contribute meaningful weight to the result.
8) When should I export the results?
Export after a valid calculation when you need documentation, reporting, sharing, or a saved snapshot of the item breakdown and summary metrics.