Quorum requirements for a referendum to be valid

Constitution

http://www.president.ee/en/republic-of-estonia/the-constitution/index.html 

? 105. The Riigikogu has the right to submit a billor other national issue to a referendum.

The decision of the people shall be made by a majority of the participants inthe voting.

A law which is passed by a referendum shall promptly be proclaimed by thePresident of the Republic. The decision of the referendum shall be binding onall state institutions. If a bill which is submitted to a referendum does notreceive a majority of votes in favour, the President of the Republic shalldeclare extraordinary elections to the Riigikogu.

ReferendumAct

https://www.riigiteataja.ee/akt/1045564

? 2. Rahvah??letuse p?him?tted

(1)Rahvah??letus on vaba, ?ldine, ?hetaoline ja otsene. H??letamine on salajane.Igal h??letajal on ?ks h??l. Rahva otsus tehakse h??letamisest osav?tnuteh??lteenamusega.

(2)Rahvah??letusest v?ib osa v?tta Eesti kodanik, kes on rahvah??letuse p?evaks saanud18-aastaseks.

(3)H??letamisest ei v?ta osa isik, kes on:
1) valimis?iguse osas teov?imetuks tunnistatud;
2) kohtu poolt s??di m?istetud kuriteos ja kannabvanglakaristust.
[RT I 2006, 30, 231 - j?ust. 14.07.2006]