Koi Weight Estimator
Free Estimator
Estimate koi weight from length and body condition
Length alone cannot determine a koi's exact weight. This estimator uses the Fulton condition-factor relationship so you can see how body condition changes the estimate instead of hiding that uncertainty.
1. Koi length
Measure from the tip of the snout to the end of the tail fin.
2. Body-condition assumption
The 1.72 reference comes from a published study of koi at its 2+ age stage. The lean/heavier presets simply bracket body shape; they are not health classifications.
Estimated body weight
A same-length koi can weigh substantially more or less depending on sex, age, conformation, season, feeding, and body condition.
For medication dosing, shipping, medical assessment, or any task where weight accuracy matters, weigh the fish rather than relying on a length estimate.
How the koi weight estimate works
Fulton's condition factor relates fish weight to the cube of total length:
Condition-factor equation
K = 100 × weight(g) ÷ length(cm)3
Rearranged for weight
weight(g) = K × length(cm)3 ÷ 100
Why K matters
Two koi with identical lengths can have different body depth and mass, so changing K changes the estimated weight.
Estimator limitation
This is a general body-mass estimate, not a validated growth chart for every koi variety and age. Published koi studies show that condition factor changes with growth stage, and a separate recent predictive model was validated only for relatively small koi in a limited length range. Treat the result as an approximation.