Fish Growth & Project Weight from SGR
Grows tilapia
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Fish grow exponentially early — the specific growth rate (SGR) projects weight over time with final = start × e^(SGR/100 × days), so you can plan feeding, harvest and market size.
Project your fish growth
Next: plan harvest around day 60 when fish reach ~166 g; weigh sample batches regularly and adjust the feed ration as the biomass climbs.
Real SGR falls as fish grow and is sensitive to temperature, water quality and feed. Treat this as an upper-bound projection, not a guarantee.
Fish growth — key facts
- Formula
- final = start × e^(SGR/100 × days)
- SGR
- % body weight gained per day
- Growth
- exponential, not linear
- Higher SGR
- young fish, warm water
- Plans
- feeding, harvest, market size
- Estimate SGR
- (ln final − ln start)/days × 100
- Outputs
- final weight, gain, days, SGR
- Privacy
- Runs in your browser; nothing uploaded
Know the weight before you net the pond
Fish don't grow in a straight line — they grow in proportion to their size, so the weight curve bends upward, fastest in the early grow-out. The specific growth rate (SGR), a percentage of body weight per day, captures that compounding in one number, and the exponential formula final = start × e^(SGR/100 × days) turns it into a projected weight at any point ahead. That projection is the backbone of feeding and harvest planning.
This tool gives the projected final weight, the weight gain, the days and the SGR from your inputs. Use it to scale daily feed as biomass grows, time the harvest to hit the market size buyers want, and stagger stocking. Pair it with the Fish Feed Requirement, Fish Pond Stocking and Pond Aeration tools for a complete aquaculture plan.
Project the weight
See how big fish get over the days ahead.
Scale the feed
Match the ration to growing biomass.
Time the harvest
Hit the market size buyers pay best for.
Model exponential growth
SGR captures fast early grow-out.
Frequently Asked Questions
What does this calculator do?+
It projects how heavy your fish will be after a set number of days, given a starting weight and a specific growth rate. Because young fish grow exponentially, it uses final = start × e^(SGR/100 × days). The projected weight lets you plan feeding, time the harvest and aim for the right market size.
What is specific growth rate (SGR)?+
SGR is the percentage of body weight a fish gains per day, the standard way to express growth in aquaculture. It captures the exponential nature of fish growth in a single rate: a fish growing at 3% SGR adds 3% of its current weight every day, so the actual grams added rise as the fish gets bigger.
What is the growth formula?+
Final weight = start weight × e^(SGR/100 × days), where e is the natural exponential. SGR is a percentage per day, so dividing by 100 converts it to a daily fraction, multiplying by days gives the total exponent, and the exponential turns it into a growth multiplier applied to the starting weight.
Why is fish growth exponential, not linear?+
A fish gains weight roughly in proportion to its current size, so as it grows it adds more grams per day even at the same SGR. That compounding makes the weight curve bend upward over time rather than rise in a straight line — which is exactly what the exponential SGR model captures, especially in the fast early grow-out phase.
Where do I get the SGR to enter?+
You can estimate SGR from a weigh-and-compare: SGR = (ln(final) − ln(start)) / days × 100 using two known weights and the days between them. Otherwise use a published figure for your species, water temperature and stage — SGR is higher for young fish in warm, well-fed conditions and tapers as fish approach market size.
How does projected weight help with feeding?+
Feed is usually a percentage of biomass, and biomass is number of fish times their weight. Knowing the projected weight at each point lets you scale the daily ration as the fish grow, so you neither underfeed and slow growth nor overfeed and waste feed and foul the water.
How does it help time the harvest?+
Markets want a target size. By projecting weight forward, you can read off roughly when the fish reach the size buyers pay best for, line up the harvest and stagger stocking so batches mature when you want them — instead of finding out only when you net the pond.
Does temperature affect the projection?+
Strongly. Fish are cold-blooded, so growth speeds up in warm water within the species' range and slows in cold. The SGR you enter should reflect your actual conditions; if the water cools, real growth will fall below a warm-water SGR. Re-estimate SGR seasonally for the most accurate projection.
Are the figures precise?+
They're solid planning figures from a clean exponential model. Real growth depends on species, temperature, water quality, feed quality and stocking density, and SGR itself falls as fish mature. Re-weigh a sample periodically, update your SGR, and treat the projection as a plan you steer — not an exact forecast.
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