THE NUMBERS, EXPLAINED
How to use this calculator.
Adds a percentage allowance to straight spans plus one lead, then adds a purchasing spare. This is length planning only; electrical loading, outdoor rating and safe support need separate checks.
Start with your inputs
Enter anchor-to-anchor spans (m), sag allowance (%), unlit lead length (m), usable length per string (m), spare allowance (%). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Anchor-to-anchor spans (m) | 8,10,8 |
| Sag allowance (%) | 8 |
| Unlit lead length (m) | 5 |
| Usable length per string (m) | 15 |
| Spare allowance (%) | 5 |
A worked example
With the example inputs above, installed route length (m) is 33.08. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Installed route length (m) | 33.08 |
| Purchase length with spare (m) | 34.734 |
| Strings required | 3 |
How this is calculated
Installed route length (m)
Sum spans × (1 + sag percentage/100), then add one unlit lead.
Purchase length with spare (m)
Multiply route length by (1 + spare percentage/100).
Strings required
Round up purchase length ÷ usable length per string.
Symbols and units
- a
- Anchor-to-anchor spans (m)
- b
- Sag allowance (%)
- c
- Unlit lead length (m)
- d
- Usable length per string (m)
- e
- Spare allowance (%)
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions and limits
Adds a percentage allowance to straight spans plus one lead, then adds a purchasing spare. This is length planning only; electrical loading, outdoor rating and safe support need separate checks.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Installed route length (m); Purchase length with spare (m); Strings required. The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Adds a percentage allowance to straight spans plus one lead, then adds a purchasing spare. This is length planning only; electrical loading, outdoor rating and safe support need separate checks.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Further reading
OpenStax: percentages and proportions ↗
Background reading; this does not imply endorsement or independent review of SumFizz.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
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