The following calculator is based on a JavaScript implementation of the Kell equation at
Enter the temperature in °C and press the Calculate button to get the density of water at atmospheric pressure:
Molar Vol./mL:
The Kell equation, employed by the calculator, is, in MathML mark-up [supported by Firefox and Safari]:

ρH2O = ( ( ( (a T+b) T+c) T+d) T+e) T+f 1+gT
ρH2O is the density of water in kg/m3. T is the temperature in °C. The coefficients are a=-2.805425310-10 , b=1.055630210-7 , c=-4.617046110-5 , d=0.0079870401 , e=16.945176 , f=999.83952 and g=0.01687985 . A molar mass of MH2O=18.0153 g/mol is used to calculate the molar volume corresponding to the density value.

Do it right! Otherwise... will be assisted by an explaining error code in the density field as a result of entering an unacceptable temperature value:

E0010: entered value below applicable temperature range.
E0019: entered value above applicable temperature range.
E0090: unacceptable temperature value.
E0111: unresolved failure during calculation.

Good to know:
Experimental density data for liquid water at atmospheric pressure are mostly available for the temperature range from 0 °C to 100 °C. But liquid water can exist at 1 atm from about -40 °C to above 300 °C. The applicable temperature range for the above calculator is -30 °C to 150 °C, the range over which Kell provides tabulated, calculated density values along with other volume properties of water at 1 atm (Table III in [1]). The Kell equation has been employed in modeling the density of aqueous electrolyte solutions [2].

Bibscope-enhanced References
[1] Density, Thermal Expansivity, and Compressibility of Liquid Water from 0° to 150°C: Correlations and Tables for Atmospheric Pressure and Saturation Reviewed and Expressed on 1968 Temperature Scale J. Chem. Eng. Data, 1975, 20 (1), pp. 97-105. DOI: 10.1021/je60064a005.
[2] Model for Calculating the Density of Aqueous Electrolyte Solutions J. Chem. Eng. Data, 2004, 49 (5), pp. 1141-1151. DOI: 10.1021/je0498659.