NumberTally Slope Calculator
Find the slope between two points — shown as a simplified fraction and as a decimal. Enter (x1, y1) and (x2, y2); the rise, run, slope, line equation, and intercepts update instantly, with a plotted graph. Free, no sign-up.
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Rise over run
Slope measures steepness: m = rise ÷ run = (y₂ − y₁) ÷ (x₂ − x₁). Positive slope climbs left-to-right, negative slope falls, zero slope is flat, and a vertical line has undefined slope (you'd divide by zero). The fraction form (like ⁴⁄₃) is exact; the decimal is its approximation.
From slope to equation
Once you have the slope m, the line's equation is y = mx + b, where b is the y-intercept — found by plugging in either point: b = y₁ − mx₁. Parallel lines share the same slope; a perpendicular line's slope is the negative reciprocal (−1/m).
Frequently Asked Questions
What is the slope formula?
m = (y₂ − y₁) / (x₂ − x₁) — the change in y divided by the change in x, a.k.a. "rise over run."
What does a fractional slope like 4/3 mean?
For every 3 units you move right, the line rises 4 units. Fractions are exact; 1.333… is the same slope rounded.
What does it mean when the slope is undefined?
The line is vertical (x₁ = x₂), so run = 0 and division by zero is impossible. The "equation" is simply x = constant.
Does the order of the two points matter?
No — swapping the points flips the signs of both rise and run, and the two negatives cancel. You'll get the same slope either way.
How do I find a perpendicular slope?
Take the negative reciprocal: if m = 2, the perpendicular slope is −½. Their product is always −1 (except for horizontal/vertical pairs).