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Sight Height and Zero Distance: What They Change Up Close and Far Away

A 1.5 vs 2.5 inch scope height and a 100 vs 200 yard zero, solved from 5 to 1,000 yards: big holds up close, a constant offset far away, and the sight height mistake that costs a click at 1,000.

7 min readSolved with the Ballista engineUpdated October 2026

Raise the scope an inch and a 100-yard zero stops being a crossing. With 2.5 in of sight height the 6.5 Creedmoor’s bullet climbs to meet the line of sight at 100 yards and turns down without ever going above it. With 1.5 in, it crosses upward at 60 yards and peaks 0.10 in high. Up close the same inch moves your impact by about an inch. At 1,000 yards it changes the come-up by 0.25 mil, and that difference only costs you a hit if the number in your calculator is wrong.

What sight height is

Sight height is the distance from the center of the bore to the center of the scope. On a bolt rifle with low rings it’s often around 1.5 in. Tall rings, a riser rail or a large objective push it toward 2 in, and an AR-style rifle with a flat-top receiver often sits around 2.5 in. The bullet starts that far below the line of sight, and the bore has to be tilted up to bring it back to the crosshair at the zero distance. The trajectory basics article draws the geometry.

So the two numbers work as a pair. Sight height sets how far below the crosshair the bullet starts. Zero distance sets where it comes back.

Up close, sight height is the hold

Inside 50 yd the bullet hasn’t fallen much, so its position is set almost entirely by where it started: under the scope.

At 10 yd the bullet lands 1.1 in low with a 1.5 in sight height and 2.0 in low with 2.5 in. The zero distance barely matters this close: the 200 yd zero has tilted the bore up more, so it takes back a few tenths. This is the number to know for a close shot through a gap in brush, a small steel plate at a short-range stage, or a shot from prone over a rock or a barricade edge. The crosshair may be clear when the bore isn’t, and the bore is the one that counts.

The near crossing moves a long way

The near crossing is where shortcuts like “zero at 50 and you’re on at 200” come from. The engine shows how much they depend on sight height:

• With 2.5 in of sight height, a 50 yd zero crosses back down at 194 yd. The shortcut works.
• With 1.5 in, the same 50 yd zero comes back down at 119 yd. Hold dead on at 200 yd and the bullet lands 3.3 in low.

That’s why a rule that’s reliable on one rifle fails on the next. If you zero short to save a trip to the long range, run your own numbers for your own sight height and confirm at the real distance.

Far away, sight height is a constant angle

Past a few hundred yards, sight height stops mattering in inches and shows up as an almost fixed angle.

With a 100 yd zero the 2.5 in setup needs 0.25 mil less at 1,000 yd than the 1.5 in setup. With a 200 yd zero the gap is 0.11 mil. The geometry explains it. With the taller sight the bore has to climb one extra inch by the zero distance. One inch at 100 yd is about 0.28 mil, and one inch at 200 yd is half that. Far downrange, that extra tilt is almost all that’s left.

This doesn’t make a tall scope “shoot flatter” in any useful sense. Both rifles hit the same target with the right come-up. The difference is only in the numbers you dial, and your calculator handles it, provided you give it the right sight height.

The mistake: a wrong sight height in the calculator

Here’s where sight height costs real hits. The rifle is zeroed on paper, so its real trajectory is right. If the calculator thinks the scope sits higher or lower than it does, every come-up past the zero is off by that constant angle, and close shots are off by the full height error.

An easy slip is measuring to the top of the scope tube, or the bottom, instead of its center. On a 1 in tube that’s half an inch. The chart below shows what half an inch costs when the real sight height is 1.5 in and the calculator has 2.0 in.

At 1,000 yd that’s 0.12 mil with a 100 yd zero: more than a 0.1 mil click, and in the same direction on every shot. With a 200 yd zero it’s 0.06 mil. Truing would eventually absorb the error into muzzle velocity or BC, where it would then distort everything else. It’s far easier to measure carefully.

Zero distance: what it really changes

Zero distance rotates the whole trajectory through a fixed angle, so come-ups for a 100 and a 200 yd zero differ by a constant at every range. What does change:

• Inside the zero: a 200 yd zero puts the bullet up to 2.0 in above the crosshair with a 1.5 in sight. A 100 yd zero keeps it within a tenth of an inch from 60 to 100 yd.
• Sensitivity to a wrong sight height: halved with a 200 yd zero, as shown above.
• How precise the zero is: a group fired at 100 yd is tighter in inches and less moved by wind and mirage than one fired at 200, so the angle you set is usually more certain.

A zero set “2 in high at 100 yd” is just another zero distance. With a 1.5 in sight that rifle crosses the line of sight again at 205 yd, almost exactly a 200 yd zero, and a calculator can treat it either way as long as it knows which.

In Ballista the rifle profile has a Sight height field, with a note under it on how to measure: center of the bore to center of the scope. The Zero section takes the Zero distance and an “Impact above aim at zero” for a rifle zeroed high, and it keeps the air you zeroed in, so the app can show how a change of weather or altitude moves your impact.

A routine for setting these up

1. Measure sight height to the center of the scope tube. With calipers: from the top of the scope tube down to the top of the bolt shroud or receiver, then subtract half the tube diameter and add half the shroud or receiver width.
2. Pick a zero you can confirm precisely. For dialing, 100 yd is the usual choice. For holding on game, a longer zero or a zero set high at 100 yd keeps the bullet near the crosshair farther out.
3. If you zero short, check where your own rifle’s far crossing really lands before trusting a shortcut.
4. Know your close-range offset. At 10 yd the bullet is low by most of your sight height.