From《史記 – Shiji》《廉頗藺相如列傳》,

趙惠文王時，得楚和氏璧。秦昭王聞之，使人遺趙王書，願以十五城請易璧。趙王與大將軍廉頗諸大臣謀：欲予秦，秦城恐不可得，徒見欺；欲勿予，即患秦兵之來。計未定，求人可使報秦者，未得。宦者令繆賢曰：「臣舍人藺相如可使。」王問：「何以知之？」對曰：「臣嘗有罪，竊計欲亡走燕，臣舍人相如止臣，曰：『君何以知燕王？』臣語曰：『臣嘗從大王與燕王會境上，燕王私握臣手，曰「願結友」。以此知之，故欲往。』相如謂臣曰：『夫趙彊而燕弱，而君幸於趙王，故燕王欲結於君。今君乃亡趙走燕，燕畏趙，其勢必不敢留君，而束君歸趙矣。君不如肉袒伏斧質請罪，則幸得脫矣。』臣從其計，大王亦幸赦臣。臣竊以為其人勇士，有智謀，宜可使。」於是王召見，問藺相如曰：「秦王以十五城請易寡人之璧，可予不？」相如曰：「秦彊而趙弱，不可不許。」王曰：「取吾璧，不予我城，柰何？」相如曰：「秦以城求璧而趙不許，曲在趙。趙予璧而秦不予趙城，曲在秦。均之二策，寧許以負秦曲。」王曰：「誰可使者？」相如曰：「王必無人，臣願奉璧往使。城入趙而璧留秦；城不入，臣請完璧歸趙。」趙王於是遂遣相如奉璧西入秦。

秦王坐章臺見相如，相如奉璧奏秦王。秦王大喜，傳以示美人及左右，左右皆呼萬歲。相如視秦王無意償趙城，乃前曰：「璧有瑕，請指示王。」王授璧，相如因持璧卻立，倚柱，怒髪上沖冠，謂秦王曰：「大王欲得璧，使人發書至趙王，趙王悉召群臣議，皆曰『秦貪，負其彊，以空言求璧，償城恐不可得』。議不欲予秦璧。臣以為布衣之交尚不相欺，況大國乎！且以一璧之故逆彊秦之驩，不可。於是趙王乃齋戒五日，使臣奉璧，拜送書於庭。何者？嚴大國之威以修敬也。今臣至，大王見臣列觀，禮節甚倨；得璧，傳之美人，以戲弄臣。臣觀大王無意償趙王城邑，故臣復取璧。大王必欲急臣，臣頭今與璧俱碎於柱矣！」相如持其璧睨柱，欲以擊柱。秦王恐其破璧，乃辭謝固請，召有司案圖，指從此以往十五都予趙。相如度秦王特以詐詳為予趙城，實不可得，乃謂秦王曰：「和氏璧，天下所共傳寶也，趙王恐，不敢不獻。趙王送璧時，齋戒五日，今大王亦宜齋戒五日，設九賓於廷，臣乃敢上璧。」秦王度之，終不可彊奪，遂許齋五日，舍相如廣成傳。相如度秦王雖齋，決負約不償城，乃使其從者衣褐，懷其璧，從徑道亡，歸璧于趙。

The Records of the Grand Historian (Chinese: 太史公書; pinyin: Tàishǐgōng shū), also known as the Shǐjì 史記 – (Scribe’s records), is a monumental history of ancient China and the world finished around 109 BC by the Han dynastyofficial Sima Qian after having been started by his father, Sima Tan, Grand Astrologer to the imperial court. The work covers the world as it was then known to the Chinese and a 2500-year period from the age of the legendary Yellow Emperor to the reign of Emperor Wu of Han in the author’s own time.

The Records has been called a “foundational text in Chinese civilization.” After Confucius and the First Emperor of Qin, “Sima Qian was one of the creators of Imperial China, not least because by providing definitive biographies, he virtually created the two earlier figures.” The Records set the model for the 24 subsequent dynastic histories of China. Unlike Western historical works, the Records do not treat history as “a continuous, sweeping narrative”, but rather break it up into smaller, overlapping units dealing with famous leaders, individuals, and major topics of significance.

1. 《史記 – Shiji》is a formal Chinese records, the description clearly mentioned Bi.
2.  According to  《周禮·春官·大宗伯》, bi is used for dedicated to the heaven(以蒼璧禮天).The description of King of  Zhao fasting for five days before sending the bi implies that only the bi dedicated to the heaven requires such ceremony. (趙王送璧時，齋戒五日，今大王亦宜齋戒五日).
3. To send the follower in informal dress hiding the bi using a country trail running back to Zhao( 乃使其從者衣褐，懷其璧，從徑道亡，歸璧于趙。).

Here we may be certain that it is a bi with the size in diameter smaller than the width of human body, less than 40 centimeters.