Sightline & Riser Calculator
Enter your seating geometry and get the riser height needed at every row so the whole house can see the stage.
Riser heights by row
| Row | Distance | Floor height | Riser (step up) |
|---|---|---|---|
| 1 | 20 | 0 | 0 |
| 2 | 23 | 0.9484 | 0.9484 |
| 3 | 26 | 1.9403 | 0.9919 |
| 4 | 29 | 2.9706 | 1.0303 |
| 5 | 32 | 4.0354 | 1.0648 |
| 6 | 35 | 5.1314 | 1.096 |
Total rise from row 1 to the back row: 5.1314
How the calculator works
A sightline calculation answers one question, row by row: how high does this row’s floor need to be so that a seated patron here can see over the head of the patron in the row ahead, and still see the stage? The tool works from the front row backward, using similar triangles between each row’s eye position and your chosen focal point on stage.
Because the riser needed at each row depends on the riser already built at the row in front, small early choices — your row spacing, your clearance value — compound toward the back of the house. That’s exactly why a hand-waved “just add 6 inches a row” approach tends to under-serve the back rows of a raked platform.
Frequently Asked Questions
What is a sightline C-value?
The C-value is the vertical clearance a sightline is designed to keep above the head of the person in the row ahead — commonly around 60mm (2.4in) to 100mm (4in) for a comfortable, unobstructed view. This calculator lets you set your own clearance, defaulting to about 4 inches.
How is the riser height for each row calculated?
Working from the front row back, the tool finds the eye height at each row so that a straight line from that seat to your chosen focal point on stage just clears the head of the row in front by your clearance value. The riser is simply the difference in floor height between consecutive rows.
What should I use as the focal point?
Pick the lowest point on stage the audience needs to see clearly — often the downstage floor, or an actor's eye level if most of the action happens standing. A lower focal point produces a more conservative (larger) riser, since it's the hardest point to see over a row of heads.
Why do risers get taller toward the back of the house?
Because each row is farther from the stage, a small vertical error over the head in front translates into a larger sightline error by the time it reaches the back rows. The formula compensates by increasing the riser height row by row — a real, non-linear effect you can see in the table above.
Educational planning tool only. Riser and platform construction has real safety and accessibility implications — verify any figure that matters for a real build against a qualified builder and your venue’s code requirements before you build.