We introduce alevin, an efficient pipeline for gene quantification from dscRNA-seq (droplet-based single-cell RNA-seq) data. Alevin is an end-to-end quantification pipeline that starts from sample-demultiplexed FASTQ files and generates gene-level counts for two popular droplet-based sequencing protocols (drop-seq [1], and 10x-chromium [2]). Importantly, alevin handles all processing internally, avoiding reliance on external pipeline programs, and the need to write large intermediate files to disk. Alevin adopts efficient algorithms for cellular-barcode whitelist generation, cellular-barcode correction, lightweight per-cell UMI deduplication and quantification. This integrated solution allows alevin to process data much faster (typically ∼ 10 times faster) than other approaches, while also working within a reasonable memory budget. This enables full, end-to-end analysis for single-cell human experiment consisting of ∼ 4500 cells with 335 Million reads with 13G of RAM and 8 threads (of an Intel Xeon E5-2699 v4 CPU) in 27 minutes.