Calophyllum grandiflorum is a large tree thought to be endemic to western Java, however, there have been unconfirmed occurrence reports from Central Kalimantan. It occurs in primary and secondary lowland and colline rainforest at elevations of c. 300–700 m asl. Java experienced extensive and severe deforestation during the 19^th and 20^th centuries and is estimated to have lost c. 97% of its lowland rainforest. It is suspected that its geographic range and population declined during this period. It is also suspected to have been extirpated from parts of its range, such as near Chikalong, during this timeframe. It is not known to be subject to extreme fluctuations, however, its habitat outside protected areas is highly fragmented, and this genus is known to have a pollen vector dispersal ability limited to c. 50 m. The lack of detailed population and dispersal data mean it is not possible to accurately assess the impact of habitat loss on its population size, or to determine whether the population is severely fragmented. Further research is required to assess its population size, trend, distribution and fragmentation. Based on confirmed observations, area of habitat analysis, and accounting for uncertainty regarding its occurrence in some parts of its range, it has five locations, a best estimated extent of occurrence (EOO) of c. 5,290 km², and an estimated area of occupancy (AOO) of 20–3,220 km². As such, it qualifies for the Endangered category under criterion B2 and the Vulnerable category under both criteria B1 and B2. Outside of protected areas, it is experiencing a continuing decline in the area, extent and quality of habitat driven by small scale agriculture, logging and commercial plantation agriculture. Many species of Calophyllum are also major timber crops in South East Asia and research has recently been conducted on the decay resistance of this species, with the aim to investigate its usefulness as a timber crop. If it gains popularity as a timber crop, exploitation may further threaten the species. While there is some uncertainty regarding the range and population dynamics of this species, a precautionary approach has been applied, and based on current information it is assessed as Endangered B2ab(iii).

This species is endemic to western Java, Indonesia at elevations of c. 300–700 m asl (Stevens 1980). Much of its range has undergone significant habitat transformation within recent years, especially within the vicinity of Chikalong, and it is suspected the species has been extirpated from this area. However, pending further research, ranged distribution metrics are provided. It has five locations and the best estimate for extent of occurrence is c. 5,290 km², assuming extirpation from Chikalong. Following an area of habitat analysis as per Brooks et al. (2019), its area of occupancy is best estimated to lie between 20–3,220 km². Recent studies have cited it as occurring in Central Kalimantan (Maimunah et al. 2021), however, it is not known if voucher specimens were collected, and if so, which herbarium they were deposited in. For now, these occurrences are not considered in this assessment. It has also been reported as occurring on Waigeo in Raja Ampat (Widyatmoko 2010), however, this is significantly outside the consensus view of this species' range and is considered erroneous. Further research into this species' distribution is recommended.

Java experienced extensive deforestation during the 19^th and 20^th centuries, with only an estimated 3% of lowland rainforest remaining (Smiet 1990). It is suspected the population declined during this period, however, the lack of numerical population or life history data make this challenging to accurately assess. However, it has been recorded from secondary habitats and described as locally common where it occurs (Stevens 1980). It also occurs in two protected areas, Gunung Gede-Pangrango National Park and Taman Hutan Raya Grand Forest Park, and was described as common in the latter (Backer #7328 (BO)). As such, the population is likely larger than current collections indicate. That said, the majority of its habitat outside these protected areas is restricted to small fragmented patches of secondary habitat, and research on other members of the genus indicate its pollen vector may be limited to a range of 50 m (Stevens 1980). This suggests that genetic flow between isolated habitat fragments would be low, and if further research indicates the majority of this species' population is held outside of protected areas, it would likely be severely fragmented. Further research on its population size and dynamics is recommended.

Calophyllum grandiflorum is a large tree growing to 15–28 m (Stevens 1980). Its primary habitat is lowland and colline moist rainforest over limestone (Jardin Botanique de Buitenzorg 1920, Stevens 1980), but it has also been collected from secondary forest (Backer #7328 (BO)).

Java experienced extensive deforestation throughout the 19^th and 20^th centuries with only an estimated 3% of lowland rainforest remaining (Smiet 1990) in small, isolated fragments. Outside of protected areas, deforestation is ongoing across this species' range, with an estimated decrease of c. 5% since 2000 with rates of tree cover loss being relatively consistent at c. 0.5% per annum since 2019 (Global Forest Watch 2023). Drivers of this forest loss are varied but major factors are small scale agriculture, logging and small scale commercial plantations (Austin et al. 2019). While this species has been recorded from secondary habitats, the current and continuous rates of habitat conversion and degradation are likely unsustainable for this species, and are viewed as the predominant threat. Calophyllum as a genus is also a major timber crop throughout South East Asia (Soerianegara and Lemmens 1993). Recent research has studied the decay resistance of C. grandiflorum timber, with the aim to investigate its potential as a timber product (Djarwanto et al. 2019). If the species became a widely used timber product, this may further threaten the species. 

Many species of Calophyllum are important timber crops throughout South East Asian, often being indiscriminately sold under the name Bintangor (Soerianegara and Lemmens 1993). Recent studies have investigated the resistance of C. grandiflorum to decay from foreign objects, with the aim to investigate its potential as an alternative lesser known timber species (Djarwanto et al. 2019). Further research on the use of this species is required.

This species is known to occur in the Gunung Gede-Pangrango National park and the Taman Hutan Raya Grand Forest Park, with large areas of this species' range covered by Mount Halimun Salak National Park and Indonesia's Forest Moratorium (UNEP-WCMC and IUCN 2023, Global Forest Watch 2023). While no conservation measures are known to be in place for this species, passive protection is assumed in these areas. The species is also held in ex situ plant collections (BGCI 2023), but is not known to be held in any ex situ genetic resource banks (Genesys PGR 2023, National Centre of Biotechnological Information 2023). Further representation of this species in ex-situ collections, both physical and genomic, is recommended.