Sine bar calculator
A sine bar turns an angle into a length: H = L·sin θ. Setting 15° on a 100 mm sine bar takes a 25.882 mm gauge block stack. Enter the angle to get the stack — or the stack you actually built to get the angle it truly sets. Works for sine plates and either the 100/200 mm or 5/10 in centre distances.
Accuracy falls off as the angle grows (the sine flattens), which is why setups past ~45° usually measure the complement instead.
Decimal or DMS: 12.5 or 12°30′
- Stack height H
- θ moves per 0.0001 in of stack
How it’s calculated
Stack height = L·sin(θ). In reverse, θ = asin(stack height ÷ L).
How does a sine bar set an angle?
A sine bar is a hardened bar with two precision rolls a fixed centre distance apart. Rest one roll on a surface plate and lift the other on a stack of gauge blocks, and the bar tilts to an angle whose sine is the stack height over the centre distance: H = L·sin θ. Build the stack, and the angle is set — no protractor required.
Enter the target angle and this calculator returns the exact stack height for a 100/200 mm or 5/10 in bar; enter a stack you actually built and it returns the angle it truly produces. Because sine flattens near 90°, a small block error swings the angle more as the setup steepens — which is why steep angles are usually set from the complement.