Calculator
Example Data Table
| Method | Length (cm) | Girth (cm) | Estimated Weight (kg) | Estimated Weight (lb) |
|---|---|---|---|---|
| Research | 80 | — | ~9.46 | ~20.85 |
| Research | 120 | — | ~30.51 | ~67.27 |
| Girth | 150 | 90 | ~42.04 | ~92.68 |
Examples are approximate and depend on fish condition and measurement technique.
Formula Used
- Length–Weight (research equation): W(kg) = a × FL(cm)b. This uses example parameters a = 0.00003 and b = 2.8893. Values can differ by area and season.
- Length–Girth (field estimate): W(lb) = L(in) × G(in)2 ÷ Factor. Factor 800 is a common general choice; 900 produces a more conservative estimate for slimmer fish.
How to Use This Calculator
- Select your preferred estimation method.
- Choose units and enter the fish length.
- If using the girth method, enter girth at the widest point.
- Click Calculate to view results above the form.
- Use Download CSV or Download PDF to save the calculation.
- Compare with the example table to validate your inputs.
Measurement Inputs
Accurate weight begins with consistent measurements. Keep the fish straight on a flat surface. Fork length runs from snout tip to the tail fork. Total length reaches the tail end and reads longer. For the girth method, wrap the tape at the thickest body point. Record values immediately, because busy decks create recall errors. Recheck once if the reading seems unusual.
Method Selection
The calculator provides two estimation paths for different situations. The research equation uses a length–weight relationship when only length is available. It supports quick planning for handling, icing, and transport. The length–girth method uses both dimensions and often reflects body condition better. Choose factor 800 for a general profile and 900 for slimmer shapes. Keep the same method across a batch.
Unit Handling
Units are managed to reduce conversion mistakes. Enter both measurements in centimeters or inches, never mixed. The system converts and stores both unit sets for reporting. If your tape is in inches, keep the input unit set to inches. The girth formula requires inches internally, while the research method uses centimeters for the exponent. This keeps calculations consistent across repeated entries.
Result Interpretation
Results are shown in kilograms and pounds for field use. Treat the value as an estimate, not a certified weight. Region, season, and condition can shift research parameters. Girth values also change with tape tension and placement. Use the notes panel to document unusual factors, such as partial cleaning or tail damage. For conservative planning, select factor 900 or round upward. For billing, weigh on a calibrated scale.
Recordkeeping and QA
Reliable records reduce disputes and improve forecasting. Export CSV for spreadsheets, trend checks, and audits. Use the PDF for job packets, manifests, and handover documents. A consistent workflow helps quality control: measure, calculate, export, then label the fish. Compare outputs with the example table to spot outliers. If a batch shifts, review measurement technique first. Over time, saved results build a reference library for safer handling.
FAQs
Which method should I use for dockside estimates?
Use the girth method when you can measure girth reliably. It reflects body condition better. Use the research method when girth is unavailable and you need a fast planning estimate.
Does the calculator require fork length or total length?
The research equation assumes fork length in centimeters. You may enter total length, but results can shift. For best consistency, measure and enter fork length whenever possible.
Why does the factor change the girth estimate?
Factor is a shape adjustment. A larger factor produces a lower weight estimate. Choose 800 for general use and 900 when fish appear slimmer for a conservative planning value.
Can I mix inches for length and centimeters for girth?
No. Enter both measurements in the same unit system. The calculator converts internally and outputs both units, but mixed inputs can create large errors.
How accurate are the results for billing or sales?
Treat results as estimates. For commercial billing, weigh fish on a calibrated scale. Use the calculator for planning, logging, and cross-checking measurements.
What should I do if the result looks unrealistic?
Confirm units, re-measure length straight, and check girth placement. Compare with the example table. If still odd, try the other method to sanity-check the estimate.