In principle, allometric relationships for algal growth can be applied to biomass size spectra to yield estimates of primary productivity. In practice, reported values of the scaling exponent of algal growth are variable, perhaps reflecting differences in the expression of cell size or phyletic differences or small sample size. The present study established the relationship between algal growth and size with a larger set of literature data than has been used previously, and assessed the effects of expression of cell size and of gross taxonomic differences on that relationship. I was able to collect a data set consisting of 127 observations of daily growth rate and cell size from three algal divisions (Chlorophyta, Chrysophyta, Pyrrophyta) and five classes (Bacillariophyceae, Chlorophyceae, Chrysophyceae, Dinophyceae and Prymnesiophyceae). Growth rate (μ, in divisions day−1) varies with cell carbon content (pg C cell−1) as μ = 3.45C−0.21. The size effect (as reflected by the exponent) is smaller if algal size is expressed as cell volume, reflecting changes in cell composition with size. The exponent is not affected by taxonomic affiliation, but growth rates of Pyrrophyta and Dinophyceae (a class within Pyrrophyta) were significantly lower than those of other divisions and classes. However, pyrrophytes have such a small size range in this data set that no meaningful growth-size relationship can be developed for that group alone.