The size and dimensions of the treasures are heavily debated. According to British scientist, historian and sinologist Joseph Needham, the purported dimensions of the largest of these ships were 135 metres (440 ft) by 55 metres (180 ft), which would make them at least twice as long as the largest European ships at the end of the sixteenth century. In fact, such dimensions would make the treasure ships larger than the largest wooden boats ever built, even 19th century steel-reinforced ones. These dimensions have thus been challenged, on engineering grounds by experts  and on the reliability of their sources (the first reference to Zheng He's ship length are from a novel dating more than a hundred years after Zheng He's voyage); some have claimed they could not have been more than 60-75 metres (195-245 ft) or that they could only have been used on special occasions in the relative safety of the lower Yangtze River. In 1962 a large rudder post was unearthed in the Treasure Ship Yard in Nanjing. As it is 11 metres long, it has been claimed that such dimensions correspond with a 200 metres (660 ft) long ship, although objections have again been raised.
The History of Ming (1739) credits the first voyage with 62 treasure ships crewed by 27,800 men.. A Zheng He era inscription in the Jinghai Temple in Nanjing gave the size of Zheng He ships in 1405 as 2,000 lia (500 tons), but did not give the number of ships 
Alongside the treasures were also another 255 ships according to the Shuyu Zhouzilu (1520), giving the combined fleet of the first voyage a total of 317 ships. However, the addition of 255 ships is a case of double accounting according to Edward L. Dreyer, who notes that the Taizong Shilu does not distinguish the order of 250 ships from the treasure ships. As such the first fleet would have been around 250 ships including the treasure ships.
The Xingcha Shenglan states that the fourth voyage consisted of 63 treasure ships crewed by 27,670 men.
There are no sources for number of ships or men for the fifth and sixth voyages.
According to the Liujiagang and Changle Inscriptions, the seventh voyage had "more than a hundred large ships"..
The most contemporary non-Chinese record of the expeditions is an untitled and anonymous annalistic account of the then-ruling Ras?lid dynasty of Yemen, compiled in the years 1439-1440. It reports the arrival of Chinese ships in 1419, 1423, and 1432, which approximately correspond to Zheng He's fifth, sixth, and seventh voyages. The 1419 arrival is described thus:
Arrival of Dragon-ships [mar?kib al-zank] in the protected harbour city [of Aden] and with them the messengers of the ruler of China with brilliant gifts for his Majesty, the Sultan al-Malik al-N?sir in the month of l'Hijja in the year 821 [January 1419]. His Majesty, the Sultan al-Malik al-N?si?'s in the Protected D?r al-Jund send the victorious al-Mahaa to accept the brilliant gifts of the ruler of China. It was a splendid present consisting of all manner of rarities [tuhaf], splendid Chinese silk cloth woven with gold [al-thiy?b al-kamkh?t al-mudhahhabah], top quality musk, storax [al-d al-rat?] and many kinds of chinaware vessels, the present being valued at twenty thousand Chinese mithq?l [93.6 kg gold]. It was accompanied by the Q?di Waj?h al-D?n ?Abd al-Rahman b. Jumay. And this was on 26 Muharram in the year 822 [March 19, 1419].
His majesty, the Sultan al-Malik al-N?sir ordered that the Envoy of the ruler of China [rusul s?hib al-Sn] returned with gifts of his own, including many rare, with frankincense wrapped coral trees, wild animals such as Oryx, wild ass, thousands of wild lion and tamed cheetahs. And they travelled in the company of Q?di Waj?h al-D?n ?Abd al-Rahman b. Jumay out of the sheltered harbour of Aden in the month of Safar of the year 822 [March 1419].
The later Yemeni historian, Ibn al-Dayba? (1461-1537), writes:
[The Chinese arrived at Aden in 1420 on] great vessels containing precious gifts, the value of which was twenty lacs [sic; lakhs] of gold... [Zheng He] had an audience with al-Malik al-N?sir without kissing the ground in front of him, and said:
"Your Master the Lord of China [s?hib al-Sn] greets you and counsels you to act justly to your subjects."
And he [al-Malik al-N?sir] said to him: "Welcome, and how nice of you to come!"
And he entertained him and settled him in the guesthouse. Al-N?sir wrote a letter to the Lord of China:
"Yours it is to command and [my] country is your country."
He dispatched to him wild animals and splendid sultanic robes, an abundant quality, and ordered him to be escorted to the city of Aden.
Shaww?l 22 [21 June A.D. 1432]. A report came from Mecca the Honored that a number of junks had come from China to the seaports of India, and two of them had anchored in the port of Aden, but their goods, chinaware, silk, musk, and the like, were not disposed of there because of the disorder of the state of Yemen. The captains of these two junks wrote to the Shar?f Barak?t ibn Hasan ibn ?Ajl?n, emir of Mecca, and to Sa?d al-D?n Ibr?h?m ibn al-Marra, controller of Judda [Jeddah], asking permission to come to Judda. The two wrote to the Sultan about this, and made him eager for the large amount [of money] that would result if they came. The Sultan wrote to them to let them come to Judda, and to show them honor.
They doe make bigger Shippes than wee do, that is to say, of 2000 tons, with five sayles, and so many mastes'.-- Niccolò Da Conti
I tell you that they are mostly built of the wood which is called fir or pine.
They have one floor, which with us is called a deck, one for each, and on this deck there are commonly in all the greater number quite 60 little rooms or cabins, and in some, more, and in some, fewer, according as the ships are larger and smaller, where, in each, a merchant can stay comfortably.
They have one good sweep or helm, which in the vulgar tongue is called a rudder.
And four masts and four sails, and they often add to them two masts more, which are raised and put away every time they wish, with two sails, according to the state of the weather.
Some ships, namely those which are larger, have besides quite 13 holds, that is, divisions, on the inside, made with strong planks fitted together, so that if by accident that the ship is staved in any place, namely that either it strikes on a rock, or a whale-fish striking against it in search of food staves it in... And then the water entering through the hole runs to the bilge, which never remains occupied with any things. And then the sailors find out where the ship is staved, and then the hold which answers to the break is emptied into others, for the water cannot pass from one hold to another, so strongly are they shut in; and then they repair the ship there, and put back there the goods which had been taken out.
They are indeed nailed in such a way; for they are all lined, that is, that they have two boards above the other.
And the boards of the ship, inside and outside, are thus fitted together, that is, they are, in the common speech of our sailors, caulked both outside and inside, and they are well nailed inside and outside with iron pins. They are not pitched with pitch, because they have none of it in those regions, but they oil them in such a way as I shall tell you, because they have another thing which seems to them to be better than pitch. For I tell you that they take lime, and hemp chopped small, and they pound it all together, mixed with an oil from a tree. And after they have pounded them well, these three things together, I tell you that it becomes sticky and holds like birdlime. And with this thing they smear their ships, and this is worth quite as much as pitch.
Moreover I tell you that these ships want some 300 sailors, some 200, some 150, some more, some fewer, according as the ships are larger and smaller.
They also carry a much greater burden than ours.-- Marco Polo
People sail on the China seas only in Chinese ships, so let us mention the order observed upon them.
There are three kinds: the greatest is called 'jonouq', or, in the singular, 'jonq' (certainly chuan); the middling sized is a 'zaw' (probably sao); and the least a 'kakam'.
A single one of the greater ships carries 12 sails, and the smaller ones only three. The sails of these vessels are made of strips of bamboo, woven into the form of matting. The sailors never lower them (while sailing, but simply) change the direction of them according to whether the wind is blowing from one side or the other. When the ships cast anchor, the sails are left standing in the wind...
These vessels are nowhere made except in the city of Zaytong (Quanzhou) in China, or at Sin-Kilan, which is the same as Sin al-Sin (Guangdong).
This is the manner after which they are made; two (parallel) walls of very thick wooden (planking) are raised, and across the space between them are placed very thick planks (the bulkheads) secured longitudinally and transversely by means of large nails, each three ells in length. When these walls have thus been built, the lower deck is fitted in, and the ship is launched before the upper works are finished.
The pieces of wood, and those parts of the hull, near the water (-line) serve for the crew to wash and to accomplish their natural necessities.
On the sides of these pieces of wood also the oars are found; they are as big as masts, and are worked by 10 to 15 men (each), who row standing up.
The vessels have four decks, upon which there are cabins and saloons for merchants. Several of these 'misriya' contain cupboards and other conveniences; they have doors which can be locked, and keys for their occupiers. (The merchants) take with them their wives and concubines. It often happens that a man can be in his cabin without others on board realising it, and they do not see him until the vessel has arrived in some port.
The sailors also have their children in such cabins; and (in some parts of the ship) they sow garden herbs, vegetables, and ginger in wooden tubs.
The Commander of such a vessel is a great Emir; when he lands, the archers and the Ethiops march before him bearing javelins and swords, with drums beating and trumpets blowing. When he arrives at the guesthouse where he is to stay, they set up their lances on each side of the gate, and mount guard throughout his visit.
Among the inhabitants of China there are those who own numerous ships, on which they send their agents to foreign places. For nowhere in the world are there to be found people richer than the Chinese.-- Ibn Battuta
On 4 September 1403, 200 "seagoing transport ships" were ordered from the Capital Guards in Nanjing.
On 1 March 1404, 50 "seagoing ships" were ordered from the Capital Guards.
In 1407, 249 vessels were ordered "to be prepared for embassies to the several countries of the Western Ocean".
On 14 February 1408, 48 treasure ships were ordered from the Ministry of Works in Nanjing. This is the only contemporary account containing references to both treasure ships and a specific place of construction. Coincidentally, the only physical evidence of treasure ships comes from Nanjing.
On 2 October 1419, 41 treasure ships were ordered without disclosing the specific builders involved.
Li Zhaoxiang's Longjiang Chuanchang Zhi (1553), also known as the Record of the Dragon River Shipyard, notes that the plans for the treasure ships had vanished from the ship yard in which they were built.
Edward L. Dreyer claims that Luo Maodeng's novel is unsuitable as historical evidence.. The novel contains a number of fantasy element; for example the ships were "constructed with divine help by the immortal Lu Ban" 
According to the History of Ming, completed in 1739, the treasure ships were 44 zhang, 4 chi, i.e. 444 chi in length, and had a beam of 18 zhang. The dimensions of ships are no coincidence. The number "4" has numerological significance as a symbol of the 4 cardinal directions, 4 seasons, and 4 virtues. The number 4 was an auspicious association for treasure ships.. These dimensions first appeared in a novel published in 1597, more than a century and a half after Zheng He's voyages. The 3 contemporary accounts of Zheng He's voyages do not have the ship dimensions. 
The zhang was fixed at 141 inches in the 19th century, making the chi 14.1 inches. However the common Ming value for chi was 12.2 inches and the value fluctuated depending on region. The Ministry of Works used a chi of 12.1 inches while the Jiangsu builders used a chi of 13.3 inches. Some of the ships in the treasure fleet, but not the treasure ships, were built in Fujian, where the chi was 10.4 to 11 inches. Assuming a range of 10.5 to 12 inches for each chi, the dimensions of the treasure ships as recorded by the History of Ming would have been between 385 by 157.5 feet and 440 by 180 feet (117.5 by 48 metres, and 134 by 55 metres).
The contemporary inscription of Zheng He's ships in the Jinghai temple inscription in Nanjing gives sizes of 2,000 liao (500 tons) and 1,500 liao(275 tons) , which are far too low than would be implied by a ship of 444 chi (450 ft). In addition, in the contemporary account of Zheng He's 7th voyage by Gong Zhen, he said it took 200 to 300 men to handle Zheng He's ships. Ming minister Song Li indicated a ratio of 1 man per 2.5 tons of cargo, which would imply Zheng He's ships were 500 to 750 tons .
The inscription on the tomb of Hong Bao, an official in Zheng He's fleet, mentions the construction of a 5,000 liao displacement ship , and taking the liao to be 500 lbs , that would be 1,250 tons displacement or around 750 tons burden.
Some scholars have argued on engineering grounds that it is highly unlikely that Zheng He's ship was 140 metres (460 ft) in length, some estimating that it had a maximum size of 110-124 m (390-408 feet) long and 49-51 m (160-166 feet) wide instead while others put them as 61-76 m (200-250 feet) in length.
One explanation for the colossal size of the 44 largest Zhang treasure ships, if in fact built, was that they were only for a display of imperial power by the emperor and imperial bureaucrats on the Yangtze River when on court business, including when reviewing Zheng He's actual expedition fleet. The Yangtze River, with its calmer waters, may have been navigable for such large but unseaworthy ships. Zheng He would not have had the privilege in rank to command the largest of these ships. The largest ships of Zheng He's fleet were the 6 masted 2000-liao ships. This would give burthen of 500 tons and a displacement tonnage of about 800 tons.
The keel consisted of wooden beams bound together with iron hoops. In stormy weather, holes in the prow would partially fill with water when the ship pitched forward, thus lessening the violent turbulence caused by waves. Treasure ships also used floating anchors cast off the sides of the ship in order to increase stability. The stern had two 2.5 m (8 foot) iron anchors weighing over a thousand pounds each, used for mooring offshore. Like many Chinese anchors, these had four flukes set at a sharp angle against the main shaft. Watertight compartments were also used to add strength to the treasure ships. The ships also had a balanced rudder which could be raised and lowered, creating additional stability like an extra keel. The balanced rudder placed as much of the rudder forward of the stern post as behind it, making such large ships easier to steer. Unlike a typical fuchuan warship, the treasure ships had nine staggered masts and twelve square sails, increasing its speed. Treasure ships also had 24 cast-bronze cannons with a maximum range of 240 to 275 m (800-900 feet). However, treasure ships were considered luxury ships rather than warships. As such, they lacked the fuchuan's raised platforms or extended planks used for battle.
Some of the drydocks at Longjiang Shipyard at Nanjing--known informally as the Treasure Ship Yard--were 27 to 36 m (90 to 120 feet) wide. But two such drydocks measured 64 m (210 feet) wide, considered large enough to build a ship 50 m (166-foot) wide.
In 1962, a large rudderpost indicating a rudder area of 452 square feet was unearthed at the Longjiang Shipyard. It has been widely said dimensions of this rudderpost corresponds with a ship of between 538 and 600 feet in length, lending credence to the notion that ships of these dimensions were indeed built. However, such use of this piece of archeological evidence rests upon supposing proportions between the rudder and the length of the ship, which have also been the object of intense contestation.
A 71.1-metre (233.3 ft) replica of a treasure ship was announced in 2006 to be completed in time for the 2008 Olympic Games. However, the replica was still under construction in Nanjing in 2010. A new date of completion was set for 2013; when this dateline failed to be met in 2014, the project was put on hold indefinitely.