How Big Are Seahorses? From Pygmy to Giant…

Seahorses are the most unique fish you will see in an aquarium because they are shaped like a horse and swim upright. One of the most confusing questions, you can search on google is, how big are seahorses?

There have been at least 56 different known species of seahorses( now, depending on which website you look at. Google hasn’t even updated their info at the time of this writing, so it can be confusing.

If you do a google search on ‘how big are seahorses’ it says 1.5 to 35.5 cm (5⁄8 to 14 in) – according to Wikipedia, but if you look up the smallest and biggest seahorses, their sizes fall outside this range, so we will try to answer the question for you to the best of our ability…

Seahorses from the 56 different reported species range in size from the smallest at an average of 1.38 cm or .54 inches of an inch to the largest seahorse ever recorded at 36 cm or 14.17 inches. The smallest species of seahorse is Satomi’s pygmy sea horse which averages 13.8 mm, 1.38 cm, or .54inches. The largest seahorse ever recorded is a pacific seahorse, also known as giant seahorses, at 36 cm or 14.17 inches.

So, there you have it. We have also put together a table for you to look at if you want to research different size seahorses for an aquarium or other reasons. This is not every seahorse species, but most of the well-know seahorse species:

Zebra Seahorseup to 8 cm
Dwarf Seahorse2 inches (51 mm) in length
Short Snouted Seahorsesup to 15 cm in length
Long Snouted Seahorsesmax 6.9 inches (17.5 cm) in height
Lined Seahorses5-6 inches but maxes out at 8 inches
Big Belly Seahorses7 inches (18 cm)
Yellow Seahorses17-30 cm
Pacific Seahorseslargest ever recorded at 14 inches
Spiny Seahorsesmaximum length of 15–17 cm
Pygmy Seahorses0.55 to 1.06 inches (1.4 to 2.7 cm)
White’s Seahorsesmaximum length of 16 cm
Barbour’s Seahorses11–15 centimeters (4.3–5.9 in)
Denise’s Pygmy Seahorsesmaximum 2.4 cm
Tiger Tail Seahorsesmaximum size of 6”
Great Seahorses11 inches (28 cm)
Flat Faced Seahorses22 cm
Japanese Seahorsesmaximum length of 8.0 cm
Hedgehog Seahorses12.5 centimeters (4.9 in) long
Knysna Seahorses12cm in length
Crowned Seahorses6 centimetres (2.4 in) – 10.8 centimetres (4.3 in)
Knobby Seahorses10 centimeters (3.9 in)”
Satomi’s Pygmy Seahorses13.8 millimeters (0.54 in)
Réunion Seahorses5.51 inches – 5.91″”(14cm – 15cm)”
Giraffe Seahorses10 centimeters (3.9 in)
South African Pygmy Seahorses2 centimeters
Jayakar’s Seahorses5.51 inches”(14 cm)”
Narrow-Bellied Seahorses16 centimetres (6.3 in) – 22 centimetres (8.7 in)
Bullneck Seahorsesup to 2.17inches”(5.5 cm)”
Shiho’s Seahorses10.8 cm
Fisher’s Seahorses8 centimeters (3.1 in)
Lichtenstein’s Seahorses4.0 cm
Tiger-Snout SeahorseAround 5 inches but up to 10 inches max.
Big-Head Seahorsesup to 35 cm (14 in)

How Big Is The Biggest Seahorse? Are There Giant Seahorses?

The biggest seahorses known are the pacific seahorses, also known as giant seahorses, with the biggest seahorse ever recorded from their species at 36 cm or 14 inches in length.

Its scientific name Hippocampus ingen comes from the greek roots ‘hippos’ – horse and ‘campus’ sea monster, which seems fitting compared to the size of many small seahorses. These seahorses are the only seahorses found in fond in the eastern pacific ocean.

Pretty much the same size are big-bellied seahorses, reaching up to 35 cm which is one shy of the 36 cm record set by the pacific seahorse. Big-bellied seahorses are found in the waters by Australia and New Zealand.

What’s The Smallest and Second Smallest Seahorse

The smallest seahorse recorded to date is Satomi’s pygmy sea horse(Hippocampus satomiae) with an average size of 13.8 mm, 1.38 cm, or .54inches.

These species weren’t named as an official species until 2008 and were named after Satomi Onishi, the diver who discovered them. They live in the waters by an island called Derawan Island by Kalimantan or Indonesian Borneo.

Before Satomi’s pygmy seahorse was found, the smallest seahorse was Denise’s pygmy sea horse(H. denise) which was measured at 16 mm or 0.63 inches in length.

How To Make Sure Your Seahorses Grow As Big As They Can

The most important thing you can do if you want your seahorse to grow to optimal length and size is to make sure they have clean water first, feed them right, make sure they have enough room and hitches, make sure there are no dead spots without oxygen in their water since they need very slow-moving water.

You need to do is set up a regular maintenance schedule to follow because seahorses need extremely clean water to grow to their maximum size.

Here are the things you need to do on a regular basis:

  • Clean the filter
  • Clean the protein skimmer
  • Check your water parameters: temperature, salinity, pH, calcium, phosphates, and nitrates.
  • Make sure all the equipment is still working
  • Replace 25 percent of the water in your tank
  • Remove detritus from your tank, mainly the substrate
  • Top off the tank with the proper mixture of saltwater
  • Monitor the condition of your seahorse for signs of bad health

To summarize:

Check your equipment daily

Check your water salinity two times per week

Change 25 percent of your water once or twice per month depending on the readings when you check it.

It is also recommended that you buy premixed saltwater for your seahorses or at least use distilled water when mixing your saltwater. As long as you avoid tap water, there is less chance of something bad making it into your tank. When mixing your saltwater, you need to use sea salt from a pet store or online. Measure the salinity with a hydrometer or refractometer to be close to 32ppt – 33ppt.

Feeding Your Seahorse

Most people feed their seahorses twice per day.

You should feed them brine shrimp, red or ghost shrimp, frozen Mysis, krill, spirulina flakes, or dry flaked food for seahorses.


I hope we have shown how big seahorses are or can get. If you are hoping to buy seahorses, this guide will help you research the right ones according to size.

Research is important for seahorses because they are known as one of the most difficult fishes to take care of.

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