How to use this calculator
- Enter operating assumptions that match one consistent period.
- Review units carefully and keep costs, visits, or staff time on the same basis.
- Adjust the inputs to compare a conservative and an expected scenario.
- Use the main result with the supporting metrics before making an operating decision.
Formula
Usable packs = packs on hand × (1 − damage rate) − reserve packs. Duration in weeks = usable packs ÷ packs per install ÷ installs per week.
Percent inputs are converted to decimals inside the calculation. Monetary values are rounded only for display.
What the result means
The main result summarizes the operational constraint or financial threshold implied by the current inputs. Read it together with the secondary results: a single headline number can hide the effect of utilization, waste, client mix, or fixed cost.
Use the result as a planning estimate rather than a guarantee. Actual demand, staff performance, product usage, discounts, tax, and local requirements may differ.
Example calculation
After damage allowance and a 10-pack reserve, 59.1 packs are available. That supports 11.8 full installs or 2.0 weeks.
Practical tips
- Use recent invoices, payroll burden, and appointment records instead of memory.
- Run a conservative scenario for waste, cancellations, or lower utilization.
- Keep input units consistent; do not mix weekly volume with monthly costs unless labeled.
- Recalculate after a material price, wage, service-time, or workflow change.
- Treat decimal service capacity as planning information and round down when only complete services are possible.
Input reference
| Input | Unit | Example |
|---|---|---|
| Extension packs on hand | packs | 72 |
| Packs used per full install | packs | 5 |
| Damage and unusable stock | % | 4 |
| Full installs per week | installs | 6 |
| Safety stock to keep | packs | 10 |
Frequently asked questions
Why is safety stock subtracted after damage allowance?
The calculator first removes the estimated unusable share, then protects the entered number of usable reserve packs.
Can packs from different colors be combined?
Only if they are operationally interchangeable. Otherwise, calculate each color, length, or texture separately.
How are partial installs interpreted?
A decimal indicates remaining material, but you should round down if a full client install requires complete packs.
Does the estimate include extension reuse?
No. It models new pack consumption. Reduce packs per install only if your documented workflow supports reuse.
Why can inventory duration be zero?
Usable stock may be at or below the safety reserve after applying the damage allowance.