Note 10 - Commitments and Contingencies (Details Textual) - USD ($)	Sep. 26, 2018	May 02, 2017	Dec. 30, 2015	Sep. 30, 2018
Consulting Services, Monthly Payment			$ 23,438
Consulting Services, Period of Services			4 years
Contractual Obligation, Total				$ 1,125,024
President and Chief Executive Officer [Member]
Employment Agreement, Annual Base Compensation		$ 288,603
Employment Agreement, Car Allowance Monthly		$ 800
Employment Agreement, Option, Number of Shares, Expected to Grant		3,731,322
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		10 years
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period		5 years
Employment Agreement, Common Stock, Expect to Grant, Subject to Lock-Up Agreement		1,500,000
Employment Agreement, Lock-up Agreement, Successful Commercialization, Minimum Cash Receipt		$ 3,000,000
Employment Agreement, Lock-up Agreement, Minimum Revenue Recognized		$ 3,000,000
Employment Agreement, Term		5 years
President and Chief Executive Officer [Member] | Non-Qualified Stock Option [Member]
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price		$ 0.45
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		10 years
Clyra [Member]
Debt Instrument, Extension Period	12 years
Debt Instrument, Term	1 year 180 days
Clyra Acquisition, Common Stock Redeemable for BioLargo Common Shares [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	10,000
Scion Acquisition [Member]
Business Acquisition, Shares Exchanged	33,015
Business Combination, Consideration Transferred, Liabilities Incurred	$ 1,250,000
Business Acquisition, Base Capital Requirement for Escrow Release	1,000,000
Business Acquisition, Gross Revenue, Tranche One	100,000
Business Acquisition, Gross Revenue, Tranche Two	100,000
Business Acquisition, Gross Revenue, Tranche Three	500,000
Business Acquisition, Gross Revenue, Tranche Four	1,000,000
Business Acquisition, Gross Revenue, Tranche Five	$ 2,000,000
Business Acquisition, Base Capital Receipt, Period Requirement	120 years
Scion Acquisition [Member] | Clyra [Member]
Debt Instrument, Interest Rate, Stated Percentage	5.00%
Debt Instrument, Percent of Investment Proceeds	25.00%
Debt Instrument, Percent of Gross Revenue	5.00%
Business Combination, Shares Acquired	12,755
Stock Issued During Period, Shares, Acquisitions	7,142,858
Stock Redeemed Upon Vesting of 10,000 Clyra Acquisition Shares, Shares	10,000
Scion Acquisition [Member] | Clyra Acquisition, Common Stock [Member]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	21,000