Curvature Calculator
Enter the values the curvature form asks for and the result is computed here, in the page, with no sign-up and no upload. Change one field at a time to see how sensitive the curvature figure is to that assumption.
Distance Settings
Target Settings
Calculate Horizon Distance
Line of Sight Calculator
Use the scientific calculator with steps
Why You Can’t Trust Your Eyes (And How to Fix It)
You’re standing on a cliff, camera in hand, trying to capture a perfect shot of a lighthouse 30 kilometers away. The air is clear, the sun is low — but the lighthouse looks strangely cut off at the bottom. Half of it seems to be missing. You zoom in, adjust your focus, and still, the base is gone.
That’s not a lens issue. That’s the Earth’s curve swallowing the lower part of your subject.
For photographers, surveyors, ham radio operators, and drone pilots, this optical illusion isn’t just frustrating — it can ruin a shot or a calculation. And until recently, figuring out exactly how much of something is hidden required digging out a formula, knowing the Earth’s radius, and punching numbers into a spreadsheet. Not exactly something you can do while hiking up a hill.
That’s why the Earth Curvature Calculator on heycalc.org exists. It’s a free, browser-based tool that instantly tells you your horizon distance, how much of a distant object is hidden, and whether a line of sight is clear — all without uploading a single piece of data to any server.
A Tool That Gets the “Hidden” Out of Hidden Height
The first time I used this calculator, I was trying to figure out if I could see a cell tower from my roof. I had the tower’s height (40 meters), my eye level (about 6 meters up), and the distance (12 km). Instead of Googling the formula and fumbling with a calculator, I just opened the tool, typed in the numbers, and hit “Calculate.”
Within a second, I saw:
- Horizon Distance from my height: 8.47 km (so I could only see the tower if it were that close)
- Curvature Drop at 12 km: 11.3 meters
- Hidden Height of the tower: 4.9 meters — meaning the bottom 5 meters of the tower were hidden.
- Visible Height: 35.1 meters — the rest was above the horizon.
Exactly the answer I needed. And it came with an interactive chart that showed the curvature profile, so I could visually confirm the line of sight.
That’s the beauty of this tool: it transforms a tedious math problem into a three-click answer.
Three Ways Different People Use the Same Calculator
1. Photographers and Filmmakers Planning a Shoot
When you’re scouting a location for a sunset shot over water, knowing the curvature drop helps you anticipate whether the horizon will cut through your subject. Use the Curvature Effect tab: set your observer height (where you’ll place the camera) and the distance to your subject. The calculator will tell you the hidden height — so you can decide whether to climb higher or move closer.
2. Radio Amateurs and Network Engineers Checking Line of Sight
For anyone setting up a point-to-point link — Wi-Fi bridges, microwave antennas, or even just a walkie-talkie repeater — the Line of Sight tab is indispensable. Enter transmitter height, receiver height, distance, and signal frequency. The tool calculates the maximum line-of-sight distance, signal status (clear or blocked), and even the radius of the first Fresnel zone. Engineers often use this to decide if they need a taller mast.
3. Sailors, Hikers, and Drone Pilots
Need to know how far you can see from a boat’s crow’s nest or a drone at 120 meters? The Horizon Distance tab gives you the answer in kilometers or miles, plus the viewing angle and the surface area visible. For drone operators, this is crucial for maintaining visual line of sight regulations.
The Privacy Promise: Your Data Never Leaves Your Device
I get it — when a website asks you to input distances and heights, you might wonder: Is this data being stored? Will someone see my survey coordinates?
With this calculator, the answer is a solid no. All calculations happen in your browser using JavaScript. No data is sent to any server, no cookies track your inputs, and no third-party service gets a peek at your numbers. This is especially important if you’re using it for work — say, planning a telecom installation or mapping a construction site — where confidentiality matters.
The tool even works offline after the first load. So you can bookmark it, open it in a remote area without internet, and still crunch the numbers.
Beyond the Basics: Understanding the Refraction Setting
One detail that makes this calculator stand out is the Atmospheric Refraction dropdown. Light bends when it travels through different air densities, especially near the ground. That bending can make objects beyond the geometric horizon appear slightly higher than they are.
- No Refraction: Pure geometric curve — what you’d get on a fictional planet with no atmosphere.
- Standard (7/6 Earth Radius): The most common model, used in most practical calculations — it effectively makes the Earth appear slightly “flatter.”
- Strong Refraction (6/5 Earth Radius): For extreme conditions, like hot desert air resting above cold water, which can create mirages.
For casual use (photography, hiking), “Standard” is almost always right. But if you’re doing precision work — like calculating radio coverage — switching to “No Refraction” gives you a conservative safety margin.
One Last Thing Before You Close the Tab
Every time I use this tool, I’m reminded that the Earth is round in a very practical, measurable way. The numbers don’t lie — and now you don’t have to do the algebra either. Whether you’re lining up a photo, checking a radio link, or just satisfying your curiosity about how far you can see, the heycalc.org Earth Curvature Calculator is the most straightforward, private, and reliable way to get the answer.
Bookmark it. You’ll be surprised how often you need it.
Frequently Asked Questions about Curvature Calculator
How do I sanity-check the curvature result?
Rerun the calculator with a known example and compare it against the figure you expect; then swap back to your own numbers.
Which curvature inputs change the outcome most?
Adjust one field at a time. The figure that shifts the result hardest is the assumption worth double-checking before you rely on it.
How do I calculate how far the horizon is from my eye level?
Enter your height above ground in the Horizon Distance tab. The tool instantly returns the distance to the horizon in kilometers or miles. For example, a person standing 1.7 meters tall sees the horizon at about 4.7 km (without refraction). If you’re on a 10-meter cliff, that horizon jumps to around 11.3 km.
Can I use this earth curvature calculator for engineering designs?
Yes, many civil engineers and telecom planners rely on it for preliminary line-of-sight checks. The tool includes a Line of Sight tab with Fresnel zone calculation, which is essential for point-to-point wireless links. However, for final engineering decisions, you should always verify with on-site surveys and professional software.
Is it safe to enter sensitive locations into an online curvature calculator?
Absolutely. As mentioned earlier, all processing happens in your browser. Your inputs never get transmitted over the internet. If you’re still cautious, you can even load the page, disconnect from Wi-Fi, and continue using it — the calculations work offline.
What units does the curvature drop calculator support?
Everything you’d need: kilometers, miles, meters, and feet for distances; meters and feet for heights. The results are displayed in the same units you choose, so there’s no mental conversion required.