InputTestHub

Drill Bit Size Calculator

Gives the tap drill and clearance drill size for metric threads from M3 to M16, with pitch and the major-diameter-minus-pitch rule.

Calculators Nothing uploaded No sign-up Free, unlimited
Calculators tool
Enter your figures and press Calculate.
In short Drill Bit Size Calculator is a free online tool on inputtesthub.com that gives the tap drill and clearance drill size for metric threads from M3 to M16, with pitch and the major-diameter-minus-pitch rule. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Drill Bit Size Calculator

  1. Enter your figures in the input fields.
  2. The result updates as you type, together with the full working.
  3. Check the breakdown table to see exactly how the number was reached.

About the Drill Bit Size Calculator

The Drill Bit Size Calculator gives the tap drill and clearance drill size for metric threads from M3 to M16, with pitch and the major-diameter-minus-pitch rule. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Drilling a hole to tap an M8 thread.
  • Finding the clearance size so a bolt passes freely.
  • Checking a chart before breaking a tap.

Details

M6 tap drill5.0 mm
M8 tap drill6.8 mm
M10 tap drill8.5 mm
Rulemajor diameter − pitch
Engagement≈ 75%

The maths behind it

This tool uses Tap drill diameter ≈ major diameter − pitch, which gives about 75% thread engagement. Clearance drill is the next size above the major diameter. Every intermediate value is shown on screen, so the result can be checked by hand.

The standard tap drill gives about 75% thread engagement — close to full strength and far easier to tap. Chasing 100% gains a few per cent and dramatically raises the chance of snapping the tap in a blind hole.

Frequently asked questions

Is the Drill Bit Size Calculator free?
Free, unlimited, and no email address required. You can use it a hundred times a day and nothing changes.
Can you see what I put into this tool?
No. The Drill Bit Size Calculator runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
How is the result calculated?
It uses Tap drill diameter ≈ major diameter − pitch, which gives about 75% thread engagement. Clearance drill is the next size above the major diameter. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What is the Drill Bit Size Calculator used for?
The jobs it is built for: drilling a hole to tap an M8 thread. Finding the clearance size so a bolt passes freely. Checking a chart before breaking a tap. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything to watch out for?
The standard tap drill gives about 75% thread engagement — close to full strength and far easier to tap. Chasing 100% gains a few per cent and dramatically raises the chance of snapping the tap in a blind hole.
Which values should I know?
M6 tap drill is 5.0 mm. M8 tap drill is 6.8 mm. M10 tap drill is 8.5 mm. These are printed on the page itself, so you do not have to take them on trust.
Can I rely on this for exact work?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

Related calculators tools

All 382
01

Loan Calculator

Works out the monthly payment, total interest and full repayment schedule for any loan from…

02

EMI Calculator

Calculates your Equated Monthly Instalment with a full principal-versus-interest breakdown and…

03

Mortgage Calculator

Estimates a full monthly housing payment including principal, interest, property tax…

04

Car Loan Calculator

Calculates a car finance payment from the price, deposit, trade-in, interest rate and term…

05

Personal Loan Calculator

Works out instalments and total cost for an unsecured personal loan, including any processing…

09

SIP Calculator

Projects the maturity value of a monthly Systematic Investment Plan, showing invested amount…