The ubiquitous presence of airborne microplastics (MPs) in different indoor environments prompts serious concerns about the degree to which we inhale these particles and their potential impact on human health. Previous studies have mostly targeted MP in the 20-200 µm size range, which do not penetrate into the lungs. In this study, we specifically investigate airborne, indoor suspended MPs in the inhalable 1-10 µm (MP1-10µm) range in residential and car cabin environments, by using Raman spectroscopy. The median concentration of total suspended indoor MPs for the residential environment was 523 MPs/m3 and 2,238 MPs/m3 in the car cabin environment. The predominant polymer type in the residential environment was polyethylene (PE), and polyamide (PA) in the car cabin environment. Fragments were the dominant shape for 97% of the analyzed MPs, and 94% of MPs were smaller than 10 µm (MP1-10µm), following a power size distribution law. We combine the new MP1-10µm observations with published indoor MP data to derive a consensus indoor MP concentration distribution, which we use to estimate human adult indoor MP inhalation of 3,900 MPs/day for the 10-300 µm (MP10-300 µm) range, and 68,000 MPs/day for MP1-10µm. These exposure estimates are 100-fold higher than previous extrapolated estimates. We use the observed MP size distribution to estimate adult nanoplastic (NP) inhalation for 0.1-1 µm (NP0.1-1µm) and 0.01-0.1 µm (NP0.01-0.1µm) size ranges, at 1,500,000 and 33,000,000 NPs/day.