The vocal range of people is an important topic to vocal science and speech pathology, and has of course received much research attention.
A2-C4 (adult males) and A3-C5 (others) normally work for most people, in line with both answers from Edward and Laurence Payne quoting standard practice. It's called standard for a reason.
Summary of results
Studies which are not open access are not included. Note I'm specifically going to take the most inclusive range, i.e. approx -2 stdev or 5th percentile for upper limit and +2 stdev or 95th percentile for lower limit.
Dienerowitz et al., 2021 , studying 1578 mostly untrained children, report A3-C5 for most, except about A2-C4 for older boys. Wuyts et al., 2010 , with 74 younger children report A3-E♭5.
In adults, Hunter and Titze, 2005 , reported 4 untrained subjects at G2-G♯4 (male) and D3-E5 (female). Siupsinskiene, 2010 , reports A2-G4 (untrained male, n=38; Table 2) and G3-D5 (untrained female, n=89; Table 3). Ma et al., 2007 , reports E3-G5 (non-dysphonic female, n=35; Table 2). D'Alatri and Marchese, 2014 , reports F♯3-B♭4 (non-dysphonic female, n=40; Table IV - mean used for upper limit).
Remember most of these are reporting extreme ranges, so going straight to the edge is not going to be fun for most people.
High and low voice limits of children. Figure 1 from .
Vocal and hearing ranges of single subjects. Figure 1 from .
: Tobias Dienerowitz, Thomas Peschel, Mandy Vogel, Tanja Poulain, Christoph Engel, Wieland Kiess, Michael Fuchs, and Thomas Berger. "Establishing Normative Data on Singing Voice Parameters of Children and Adolescents with Average Singing Activity Using the Voice Range Profile." Folia Phoniatrica et Logopaedica: in press, 2021.
: Floris L. Wuyts, Louis Heylen, Fons Mertens, Marc De Bodt and Paul H. Van de Heyning. "Normative voice range profiles of untrained boys and girls." Journal of Voice 24(2):153-160, 2010.
: Eric J. Hunter and Ingo R. Titze. "Overlap of hearing and voicing ranges in singing." Journal of Singing 61(4):387-392, 2005.
: Nora Siupsinskiene. "Effects of Vocal Training on Quantitative Voice Parameters in Healthy Voice Adults and Children." In Laryngeal Diseases: Symptoms, Diagnosis and Treatments, Oldrich Nemecek and Viktor Mares (eds.), Nova Science Publishers, 2010.
: Estella Ma, Jennie Robertson, Claire Radford, Sarah Vagne, Ruba El-Halabi, Edwin Yiu. "Reliability of Speaking and Maximum Voice Range Measures in
Screening for Dysphonia." Journal of Voice 21(4):397-406, 2007.
: Lucia D'Alatri, and Maria R. Marchese. "The speech range profile (SRP): an easy and useful tool to assess vocal limits." Acta Otorhinolaryngologica Italica 34:253-258, 2014.