---
type: "hub"
name: "Machining calculators"
calculator_count: 5
verified: "August 1, 2026"
url: https://shopmath.org/calculators
---

# Machining Calculators — Threads, Fits, Position and Tensile Area

5 calculators, each showing the formula it used and the standard that formula comes from. They exist for the questions a table cannot answer — a thread at an engagement no chart prints, a diameter at a fit no table lists — and every one of them states its assumptions and links back to the reference pages the numbers came from.

## The calculators

| Calculator | Input space | Standard |
| --- | --- | --- |
| [Tap Drill Size Calculator](https://shopmath.org/calculators/tap-drill.md) | 150 threads × 50–100% engagement | NBS H28 / ASME B1.1 and ISO 68-1 profile geometry |
| [Thread Engagement Calculator](https://shopmath.org/calculators/thread-engagement.md) | 150 threads × any drill or measured Ø | NBS H28 / ASME B1.1 and ISO 68-1 profile geometry |
| [ISO 286 Limits & Fits Calculator](https://shopmath.org/calculators/iso-fit.md) | 1–500 mm × 24 designations, 16 named fits | ISO 286-1 / ISO 286-2 |
| [True Position Calculator](https://shopmath.org/calculators/true-position.md) | any Δx, Δy × RFS, MMC or LMC | ASME Y14.5 · ISO 1101 |
| [Thread Tensile Stress Area Calculator](https://shopmath.org/calculators/thread-tensile.md) | 150 threads × your own strength figure | ASME B1.1 / NBS H28 and ISO 898-1 stress-area forms |

## What each one is for

- [Tap drill](https://shopmath.org/calculators/tap-drill.md) — Any of 150 inch and metric threads at any thread engagement from 50% to 100% — with the drill that actually fits and what it really leaves.
- [Thread engagement](https://shopmath.org/calculators/thread-engagement.md) — The reverse: you have a drill in your hand, or a hole already in the part. Find out what percent of thread it leaves before you run the tap.
- [ISO fit](https://shopmath.org/calculators/iso-fit.md) — Hole and shaft limits, clearance or interference, and the tolerance zones drawn to scale — any size from 1 to 500 mm, any letter and grade in the table.
- [True position](https://shopmath.org/calculators/true-position.md) — Measured X/Y deviation to a diametral position value, with MMC or LMC bonus tolerance and the pass/fail against the feature control frame.
- [Thread tensile](https://shopmath.org/calculators/thread-tensile.md) — Tensile stress area from the thread's own geometry, multiplied by the strength off your fastener's spec sheet — never by a number we could not verify.

## Calculator or chart?

A calculator earns its page when the input space is continuous; a static table wins when the input is a named entity. Nothing here duplicates a lookup a chart already answers — the two link to each other instead of competing.

| The question | Where it is answered |
| --- | --- |
| What drill for 1/4-20? | [Tap drill chart](https://shopmath.org/charts/tap-drill.md) |
| What drill for 1/4-20 at 63% thread? | [Tap drill calculator](https://shopmath.org/calculators/tap-drill.md) |
| What are the limits for H7 at 25 mm? | [ISO 286 tolerance chart](https://shopmath.org/charts/iso-tolerances.md) |
| What are the limits for H7/g6 at 137 mm? | [ISO fit calculator](https://shopmath.org/calculators/iso-fit.md) |

## Related pages

- Threads: [Screw thread reference](https://shopmath.org/threads.md)
- Drill sizes: [Drill bit size reference](https://shopmath.org/drills.md) (397 sizes in the index)
- Tolerances and fits: [ISO 286 fit reference](https://shopmath.org/fits.md)
- Geometric tolerancing: [GD&T symbol reference](https://shopmath.org/gdt.md)

---

*Source: [ShopMath](https://shopmath.org/calculators) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*