Fish Feeding Calculator - How Much to Feed Fish a Day

Problem: fish food comes without a portion in grams

Less than a gram. That is the daily food for ten small fish of 5 g each: 0.50 to 1.00 g. This fish feeding calculator puts a number on it: total fish weight times the rate veterinarians give for maintenance or growth, split into one or two feedings, with the weekly and monthly amount and how long a container of food will last.

Food that is not eaten stays in the water. PetMD lists obesity, swim bladder disorders, constipation and poor water quality as the results of improper feeding, and the Merck Veterinary Manual warns that overfeeding leads to health problems as well as a dirty tank. Without a number, the portion is a guess.

Solution: weigh the fish once, then feed by percentage

Number of fish - the fish that share the food.
Unit and average weight of one fish - grams or ounces. Put a cup of tank water on a kitchen scale, set it to zero, and add one fish with a net.
Adult or growing - adults get the maintenance rate of 1 to 2% of body weight a day, young growing fish 3 to 5%.
Water temperature - optional. Colder water adds a reminder to feed less.
Feedings a day - optional, one or two. Empty shows both splits.
Food container - optional net weight and price, for the days it lasts and the cost per month.

A number in grams. The daily amount comes from the feeding rates in the Merck Veterinary Manual, written by veterinarians from the University of Florida.

A check at the tank. PetMD's rule stays in the plan: feed what the fish eat in 2 to 5 minutes and remove the leftovers right away.

Fresher food. The calculator warns when a container would last longer than the 2 months Merck gives for keeping dried food.

Which rate fits your fish

The calculator offers two rates; the table shows when each one applies and what to change.

Situation	Rate a day	What to do
Adult fish in a stable tank	1 to 2% of body weight	Start at the low end, adjust by the 2-to-5-minute check
Young fish still growing	3 to 5%	Move to the adult rate once they reach adult size
Colder water, a pond in cool weather	less than the usual rate	Merck gives no figure; feed the low end or below and watch what is eaten
Food reaching the bottom uneaten	too much	Remove it right away and cut the next portion
Frozen or freeze-dried treats	1 to 2 times a week	Count them in the day's amount, not on top of it

Six tanks and ponds, run through the calculator

A school of small tetras. 10 fish of 0.5 g, adult. Result: 0.050 to 0.100 g a day, or 1.50 to 3.00 g a month.

A community tank. 10 fish of 5 g, adult, twice a day. Result: 0.50 to 1.00 g a day, 0.250 to 0.500 g per feeding.

Twelve tiny fish. 12 fish of 0.35 g, adult. Result: 0.042 to 0.084 g a day, less than a kitchen scale shows in whole grams.

Growing juveniles. 4 fish of 20 g, growing. Result: 2.40 to 4.00 g a day at the growth rate of 3 to 5%.

Three larger fish. 3 fish of 1.5 oz, adult. Result: 127.6 g of fish and 1.28 to 2.55 g of food a day.

A small pond in autumn. 6 fish of 8 oz, adult, cold water, food at $12.99 for 7.4 oz. Result: 13.6 to 27.2 g a day before the cold-water reduction; the container lasts 8 to 15 days and costs $25.28 to $50.56 a month at the full rate.

Quick reference by total fish weight

Food a day for the whole tank or pond, as the calculator rounds it. Total weight is the number of fish times the weight of one.

Total fish weight	Adult, 1 to 2%	Growing, 3 to 5%
10 g (0.35 oz)	0.100 to 0.200 g	0.300 to 0.500 g
50 g (1.76 oz)	0.50 to 1.00 g	1.50 to 2.50 g
100 g (3.53 oz)	1.00 to 2.00 g	3.00 to 5.00 g
250 g (8.82 oz)	2.50 to 5.00 g	7.5 to 12.5 g
1 lb (453.6 g)	4.54 to 9.07 g	13.6 to 22.7 g
5 lb (2,268 g)	22.7 to 45.4 g	68.0 to 113.4 g

Often asked by fish keepers

How much should I feed my fish per day?

For adult fish, 1 to 2% of their body weight a day according to the Merck Veterinary Manual. Ten fish of 5 g weigh 50 g together, so they need 0.50 to 1.00 g a day.

How often should fish be fed?

Once or twice a day depending on the species, according to PetMD. Splitting the same daily amount into two feedings halves each portion; it does not add food.

What does the 2-to-5-minute rule mean?

Offer only what the fish eat within 2 to 5 minutes and remove the rest right away. The grams from the calculator are a starting point; this check at the tank decides.

How do I weigh a fish?

Set a cup of tank water on a kitchen scale, zero the scale, net one fish into the cup and read the weight, then return it. Weighing one typical fish is enough for a group of the same size.

Should I feed less in winter?

Merck says the amount should be reduced in colder weather because the fish are less active. It does not give a percentage, so the calculator adds a reminder instead of a number.

How long does fish food stay fresh?

Merck advises keeping dried food on hand for no more than 2 months and buying smaller containers more often. Ten fish of 5 g take 200 to 400 days to finish a 200 g tub.

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