A Coptic Christian group has rejected a report by Egypt's official statistics agency which estimated the community's population at 5.13 million.
The Coptic Church estimates the community at 15-18 million, the Copts of Egypt Coalition said in a statement on Tuesday.
The Church's statistics are more reliable than those of the Central Agency for Public Mobilisation and Statistics (CAPMAS), because it carries out population density checks every three months, the coalition said.
Non-Orthodox Churches, which make up 5 per cent of Christians in Egypt, also carry out similar checks, the coalition added.
The 5.13 million figure quoted by CAPMAS is actually the number of Copts living abroad, not the number living inside Egypt, according to the coalition.
The report, published by CAPMAS head Abu-Bakr Al-Gendy, could affect the status of Christians under the new constitution which is being drated these days, the coalition asserted.
Gihan Sadat, wife of former president Anwar Sadat, stated during her husband's rule that Coptic Christians in Egypt numbered around 6 million, the coalition claimed, at a time when the total population was 51.7 million.
The current Egyptian population is around 85 million.