SAG Calculator

Use this SAG calculator to find sagitta from a circle's radius and diameter, or to solve back for radius or diameter. It is useful wherever an arc drop or bow height matters in layout and design.

What This SAG Calculator Helps You Do

Use this SAG calculator to find sagitta from a circle's radius and diameter, or to solve back for radius or diameter. It is useful wherever an arc drop or bow height matters in layout and design.

How to Calculate SAG Calculator

Measure the sag inputs - Enter the dimensions, density, spacing, or thickness values shown on the page.
Check the units - Keep every input in the same unit system so the result stays consistent and easy to compare.
Choose the solve mode - Select the calculation you want to run, such as weight, volume, cost, count, or angle.
Read the output - Use the main result and the extra detail rows to verify the estimate before you order materials or build.

SAG Calculator Formula

sag = R - sqrt(R^2 - (d / 2)^2)

Symbol	Definition	Unit
R	Radius of curvature	ft
d	Diameter	ft
s	Sagitta	ft

Worked Examples

USA - Arc layout check

radius: 10
diameter: 13
sagitta: 0

Result: Sagitta = 2.40 ft

Sagitta is the key number when the arc depth is known. The estimate is 2.40 ft.

UK - Curved element radius

radius: 0
diameter: 13
sagitta: 2.4

Result: Radius = 10.00 ft

Radius is useful when you know the arc drop and chord length. The estimate is 10.00 ft.

EU - Diameter from sag

radius: 10
diameter: 0
sagitta: 2.4

Result: Diameter = 13.00 ft

Diameter can be derived once the sagitta is already measured. The estimate is 13.00 ft.

GCC - Suspension check

radius: 8
diameter: 9
sagitta: 0

Result: Sagitta = 1.39 ft

A sagitta check is quick when the circle radius is the starting point. The estimate is 1.39 ft.

How to Interpret Your Results

Range	Meaning	Action
< 1 ft	Shallow sag	Usually a gentle curve or small drop.
1–3 ft	Moderate sag	Common for many practical curved layouts.
> 3 ft	Deep sag	Double-check the geometry and required clearance.

Frequently Asked Questions

It estimates the main planning quantity for sag work using the formula shown on the page. That gives you a practical number before you order materials, compare suppliers, or talk to a contractor. SAG here refers to sagitta, the depth of an arc relative to its chord.

Enter the values that match the unit labels beside the fields. If the page expects feet, inches, gallons, pounds, or watts, keep everything in that unit family so the result stays reliable.

The calculator multiplies or divides the main quantity by the values you enter, so every measurement feeds directly into the final answer. A small change in depth, area, density, or factor can make a large difference on a bigger project.

Yes, as long as the units stay consistent within the calculation. If the page expects feet, inches, gallons, or pounds, convert first so the final result is accurate and easy to interpret.

Treat the result as a planning estimate. Use the main output for sizing or ordering, then review the detail rows for waste, weight, cost, or conversion notes before you finalize the purchase.

Yes if the job involves cut losses, uneven ground, spill risk, or irregular shapes. A small allowance is usually safer than ordering exactly to the bare math, especially for sag projects that are hard to top up later.

It is exact for the numbers you enter, but real-world projects can still vary because of compaction, tolerances, site conditions, and product differences. Use the result as a solid working estimate, not a final structural or procurement check.

Yes. That is one of its main uses. The result helps you estimate how much to buy, what it may weigh, and what the budget might look like before you place an order or request a quote.

Disclaimer: This calculator provides planning estimates only. Verify the exact geometry and any structural or suspension requirements before using the result in a build.

Sources

Last reviewed: March 2026

SAG Calculator

Result

What This SAG Calculator Helps You Do

How to Calculate SAG Calculator

SAG Calculator Formula

Worked Examples

How to Interpret Your Results

Frequently Asked Questions

What does the SAG calculator estimate?

Which measurements should I enter for the SAG calculator?

Why does the SAG result change when I change one input?

Can I use metric and imperial units with the SAG calculator?

How should I read the SAG result?

Should I add waste or allowance to the SAG calculation?

Is the SAG calculator exact?

Can I use the SAG calculator for ordering materials?

Related Calculators

Sources

Share

Popular Calculators