Ruby Bay is a settlement in the Tasman District of New Zealand's upper South Island. It is located between Māpua and Tasman on Te Mamaku / Ruby Bay. Ruby Bay was named after small 'rubies' (red chert) found within the moutere gravel.

Ruby Bay is described by Statistics New Zealand as a rural settlement. It covers 4.83 km (1.86 sq mi) and had an estimated population of 850 as of June 2024, with a population density of 176 people per km. Before the 2023 census, it was part of the larger Ruby Bay-Māpua SA2 statistical area.

Historical population

Year	Pop.	±% p.a.
2006	555	—
2013	621	+1.62%
2018	678	+1.77%
Source:

Before the 2023 census, the settlement had a smaller boundary, covering 2.96 km (1.14 sq mi). Using that boundary, Ruby Bay had a population of 678 at the 2018 New Zealand census, an increase of 57 people (9.2%) since the 2013 census, and an increase of 123 people (22.2%) since the 2006 census. There were 249 households, comprising 327 males and 351 females, giving a sex ratio of 0.93 males per female, with 105 people (15.5%) aged under 15 years, 66 (9.7%) aged 15 to 29, 330 (48.7%) aged 30 to 64, and 171 (25.2%) aged 65 or older.

Ethnicities were 95.1% European/Pākehā, 6.2% Māori, 1.3% Pasifika, 0.9% Asian, and 3.5% other ethnicities. People may identify with more than one ethnicity.

Although some people chose not to answer the census's question about religious affiliation, 62.4% had no religion, 27.9% were Christian, 0.4% were Buddhist and 2.2% had other religions.

Of those at least 15 years old, 183 (31.9%) people had a bachelor's or higher degree, and 75 (13.1%) people had no formal qualifications. 138 people (24.1%) earned over $70,000 compared to 17.2% nationally. The employment status of those at least 15 was that 237 (41.4%) people were employed full-time, 93 (16.2%) were part-time, and 9 (1.6%) were unemployed.