What Is the Garden Arch Calculator?
A garden arch only looks right when its curve is a true, symmetrical arc, and cutting or bending that arc accurately starts with knowing the radius. Our free garden arch calculator turns three simple measurements into the full geometry: the span you want to cross, the rise (how tall the curve stands above the legs), and the leg height. From those it derives the arc radius, the arc length of the curved top, the overall height, and the linear feet of frame material you need to buy, so the arch comes out symmetrical the first time. It also counts pickets or slats from your chosen spacing if you want an infill figure. The geometry underneath is the circular segment formula, the same math carpenters use for any curved work: radius from span and rise, arc length from radius and angle. Whether you are bending metal conduit, laminating thin wood strips, or cutting segments from straight timber, the numbers tell you the radius to bend to and the length to cut before you start.
How to Use This Calculator
- Enter the arch span: the clear horizontal distance between the two legs.
- Enter the arch rise: how tall the curved top stands above the top of the legs.
- Enter the leg height: the vertical distance from the ground to where the curve begins.
- Set the picket or slat spacing if you want a count of infill pieces along the curve.
- Read off the arc radius, the arc length, the overall height, and the chord dimensions.
- Use the frame-material figure to buy your timber, pipe, or lattice stock, adding your usual waste margin.
- Lay out the curve on the ground using the radius (a string and a stake work well) before cutting.
Why Accurate Garden Arch Calculations Matter
An arch cut by eye is almost never symmetrical, and the eye is unforgiving about it. A curve with a slightly different radius on each side reads as lopsided from across the garden, and it cannot be fixed once the pieces are cut. The radius matters twice: it sets the shape, and it sets the arc length, which is always longer than the straight span beneath it. Builders who buy material for the span and forget the arc come up short on the curved section, especially painful with metal conduit or laminated strips that must be bent to a set radius and cannot be spliced invisibly. Knowing the radius also tells you whether the curve is bendable at all: a very tight radius will kink conduit and crack solid wood, which is a signal to use segmented or laminated construction instead. This calculator gives you the shape, the length, and the feasibility check from three measurements.
