Gutter corner miter calculator
Choose a half-round or box gutter, enter width, depth, run lengths and corner angle, and choose an inside or outside corner. You get both miter-cut gutter pieces.
Enter your measurements
Seam
580.2mm
Exact geometry
- Cut length
- In the app
- Miter curve
- In the app
- Sheet size
- In the app
Every result is in Trueflat
The free web version shows the main result and the drawing. Trueflat gives you every mark and measurement, and exports a cut sheet. It is free to download.
How to lay it out
Draw the stretch-out
Draw a base line as long as the gutter profile: πW ÷ 2 for half round, 2 × depth + W for box.
Mark the profile stations
For half round, divide the line into equal parts. For box, mark the two bottom corners at the depth and at depth + W.
Set off the miter heights
At each station, draw a line square to the base and mark the miter height h = L ± y tan γ from the straight end, as calculated for that piece.
Join the miter
Join the marks with a smooth curve for half round, or straight lines for box. That edge is the miter; the base line is the square end.
Form and join
Form both pieces to the profile and seam them along the miter. The second piece uses its own run length and the same rule.
Good to know
- FabLayout runs the same code as Trueflat; the result is exact geometry.
- Source: No published source. Each piece is an open cylinder or box profile cut by the vertical bisecting plane, developed by ordinates in closed form on the middle of the sheet; checked against an independent reference implementation in Trueflat.
Method and formula
A gutter corner joins two straight gutter runs on a vertical miter plane that bisects the corner. Each piece is an open profile cut square at one end and on the miter at the other.
- Turn δ = 180° − corner angle; miter angle γ = δ ÷ 2.
- Miter height at a profile station with sideways position y: h = L + σ × y × tan γ, measured from the square end. σ = +1 for an inside corner and −1 for an outside corner.
- Half round (width W): stretch-out πW ÷ 2, stations at equal angles round the half circle. The miter edge is a curve.
- Box (width W, depth Hd): stretch-out 2Hd + W with bend lines at both bottom corners. The miter edge is three straight lines.
On an outside corner the back edge, against the wall, is the short one: L − (W ÷ 2) tan γ. The front edge is the long one. Both pieces follow the same rule, so they meet on the same 3D curve and the pattern is exact. The miter curve readout is the true length of that joint. Inside means the water side of the gutter; inside or outside sizes are converted to the sheet middle.
Ogee (K-style) gutter profiles are not included; their front face varies by maker.
Worked example
Box gutter, W = 100 mm, Hd = 80 mm, both runs 300 mm, 90° outside corner: γ = 45°. At the stations 0, 80, 180 and 260 mm along the stretch-out the miter heights are 250, 250, 350 and 350 mm. Each piece has an area of 260 × 300 = 78 000 mm², and the miter is 80 + 100√2 + 80 = 301.42 mm long.
Questions
What is the difference between an inside and an outside corner?
An outside corner wraps round the outside of a building corner, so the wall side of the gutter is the shorter edge. An inside corner sits in a re-entrant corner and the front edge is the shorter one. Pick the one that matches the wall.
Can I use it for corners other than 90°?
Yes. Any corner angle from 60° to 170° works. The miter angle is half of the turn, so a 135° corner has a 22.5° miter.
Why is my run length rejected?
The shortest edge of each piece is L − (W ÷ 2) tan γ. It must be at least 5 mm, so a sharp corner on a wide gutter needs a longer run.
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