Conduit BendingAbout this site
Updated 2026-10-23
conduitbending.app is built by Blissom, the small studio behind the Conduit Bending Calculator app for Android. The website gives electricians and apprentices the everyday bending math for free; the app carries the full toolkit onto the job.
How the math is checked
Every calculator on this site runs the same calculation engine as the app. An automated test suite (88 tests at the last release) covers that engine. Among other things, it checks:
- Offset spacing and shrink (see the bending chart) against the field constants in Klein's bender guides (10° = 6 and 1/16", 22.5° = 2.6 and 3/16", 30° = 2 and 1/4", 45° = 1.4 and 3/8", 60° = 1.2 and 1/2") and against ideal trigonometry.
- 3-point saddle constants (2.5 and 3/16" for 45°, 2.0 and 1/4" for 60°).
- Stub-up and back-to-back marks against the published take-ups (5", 6", 8", 11"), listed on the bender deduct chart.
- Conduit fill counts (the conduit fill chart) against NEC Annex C (for example 9, 16 and 26 #12 THHN in 1/2", 3/4" and 1" EMT) and box fill against Tables 314.16(A) and 314.16(B)(1), including the 2020 rule for grounds beyond four.
- Input checks that reject angles outside the calculator’s 0–90° range and layouts that cannot be marked reliably with the selected bender and method, such as offsets whose marks fall too close together for the assumed shoe, or stubs shorter than the listed take-up with the standard arrow-mark method. Other tools or techniques may still make some of these bends.
Worked examples in the guides use values computed by the same engine.
Sample cases, computed when this page was built
These rows are not typed in. The page runs each input through the calculation engine when the site is built. It then compares the result with the source value: the field constants in Klein's bender guides, or the take-up for that size.
| Input | Output | Source value | Engine result | Match |
|---|---|---|---|---|
| Offset, 6" deep, 30° | Distance between marks | 12" | 12" | Yes |
| Offset, 6" deep, 30° | Shrink | 1-1/2" | 1-1/2" | Yes |
| Offset, 10" deep, 45° | Distance between marks | 14" | 14" | Yes |
| Offset, 10" deep, 45° | Shrink | 3-3/4" | 3-3/4" | Yes |
| Stub-up, 12" on 1/2" EMT | Arrow mark from end | 7" | 7" | Yes |
| Stub-up, 30" on 1-1/4" EMT | Arrow mark from end | 19" | 19" | Yes |
| 3-point saddle, 3" deep, 45° center, 36" to center | Center mark | 36-9/16" | 36-9/16" | Yes |
| 3-point saddle, 3" deep, 45° center | Center to outer marks | 7-1/2" | 7-1/2" | Yes |
| 3-point saddle, 4" deep, 60° center | Center to outer marks | 8" | 8" | Yes |
These tests check arithmetic and calculator behavior against published values. They do not prove that a particular bender, conduit or technique will produce the same physical bend. Real bends vary with the shoe's radius, its reference marks and spring-back. That is why every page asks you to check a mark on scrap first.
Sources
- NFPA 70, National Electrical Code: Chapter 9 Tables 1, 2, 4 and 5 and Note 7; 314.16; 358.24 (bends; the 360° limit is 358.24(B) in the 2023 edition, 358.26 in 2020 and earlier, and the 2026 edition adds 300.24 for runs that combine raceway types). Values follow the 2023 edition.
- Klein Tools Conduit Bender Guide for take-up (deduct), offset and saddle constants and the bender marks; Klein and Greenlee catalog data for the shoe radii named on the charts.
- Standard trigonometry: cosecant for the multiplier, tangent of the half angle for shrink, as derived on the formulas page.
What these tools are, and are not
They are estimating aids for trained electricians and apprentices. Always check marks against the deduct stamped on your own bender, and follow the code edition and local amendments your inspector enforces. This site is not affiliated with the NFPA or any bender manufacturer; brand names belong to their owners.
Found a mistake?
Leave a review or a question on the app's Google Play listing. Corrections are made on the site and in the app together, and the date at the top of each page shows when it was last reviewed.