In general, the SAT Math section covers topics all the way up until a student finishes basic Algebra, which is usually around 9th grade (assuming a student previously completed Pre-Algebra and Geometry). There's no trigonometry on the Math section of the SAT I: Reasoning Test.

Instead of the grade level, you should ask what is the highest level of math complexity covered. To better answer that, I've listed the various areas covered on the SAT Math section:

1) NUMBERS AND OPERATIONS: Arithmetic word problems (including percent, ratio, and proportion), Properties of integers (even, odd, prime numbers, divisibility, etc.), Rational numbers, Sets (union, intersection, elements), Counting techniques, Sequences and series (including exponential growth), Elementary number theory

2) ALGEBRA AND FUNCTIONS: Substitution and simplifying algebraic expressions, Properties of exponents, Algebraic word problems, Solutions of linear equations and inequalities, Systems of equations and inequalities, Quadratic equations, Rational and radical equations, Equations of lines, Absolute value, Direct and inverse variation, Concepts of algebraic functions, Newly defined symbols based on commonly used operations

3) GEOMETRY AND MEASUREMENT: Area and perimeter of a polygon, Area and circumference of a circle, Volume of a box, cube, and cylinder, Pythagorean Theorem and special properties of isosceles, equilateral, and right triangles, Properties of parallel and perpendicular lines, Coordinate geometry, Geometric visualization, Slope, Similarity, Transformations

4) DATA ANALYSIS, STATISTICS, AND PROBABILITY: Data interpretation (tables and graphs), Descriptive statistics (mean, median, and mode), Probability

Good luck in your studying!

I can't top that answer, so I'll just second see_n_heard's fine response.