The cheapest drill bit is often the most expensive per hole. This free calculator compares up to three DTH, top hammer or tricone bits on what they cost for each metre drilled. It counts the purchase price, the regrinds and, if you add them, the cost of rig time. Enter figures from your own drilling records to see which bit is cheaper in your rock, and how much it saves over a year.
Drill bit cost per metre calculator
Use one currency for every price. The figures filled in below are an example, not ATR prices.
Free to use. The results are only as good as the records you enter, so compare bits drilled in the same rock, on the same rig, at the same air pressure.
How to use the calculator
- Pick one currency and use it for every price.
- For each bit, enter the price you pay per bit, how many times you regrind it, and what each regrind costs.
- Enter the metres each bit drills before it is scrapped. Use the average from your records, not the best bit you ever had.
- To include rig time, add your rig’s operating cost per hour and each bit’s average penetration rate. Leave both blank to compare bit cost only.
- Read the total cost per metre. The lowest figure is the cheaper bit for that job, whatever the purchase price.
The formula
Bit cost per metre = (price + number of regrinds × cost per regrind) ÷ metres drilled before scrap
Rig time per metre = rig operating cost per hour ÷ penetration rate (m/h)
Total cost per metre = bit cost per metre + rig time per metre
Rig time covers the costs you pay for every hour the rig runs, whatever bit is on the string: fuel, the crew, the compressor and the rig’s own running and maintenance cost. When one bit drills faster, each metre takes less of that time.
Example: the dearer bit that costs less
The calculator opens with this example. Bit A costs 100 and drills 300 m. Bit B costs 130, which is 30% more, but drills 450 m, which is 50% more. Both get two regrinds at 10 each.
- Bit A: (100 + 2 × 10) ÷ 300 = 0.400 per metre.
- Bit B: (130 + 2 × 10) ÷ 450 = 0.333 per metre.
Bit B costs about 17% less per metre. Over 10,000 m a year the gap is about 667 in bit cost alone. If Bit B also drills faster, the saving in rig time is usually larger still. Bit A would have to cost less than 80 to match Bit B.
Getting numbers you can trust
The comparison is only as good as the records behind it. Keep these for every bit:
- Metres by serial number. Write the bit’s serial or batch number on the drill log and add up its metres until it is scrapped.
- Penetration rate per shift, across the whole life of the bit. A bit slows as its buttons wear.
- Each regrind, with the metres drilled between regrinds.
- Bits lost or broken early. Count them in the average. Leaving them out flatters the bit.
- The same conditions. Compare bits in the same rock, on the same rig, at the same air pressure. A bit that wins in soft limestone can lose in abrasive granite.
Grinding on time matters too. A bit run too long between regrinds drills slower and has a shorter life. Follow the regrind guide from the bit maker.
Which bits it works for
The same formula works for any bit that is bought, worn out and replaced:
- DTH button bits
- Top hammer button bits
- Tricone bits (tricone bits are not reground, so enter 0 regrinds)
- PDC and drag bits
For a DTH hammer, enter the hammer price as the price, any rebuild kits as regrinds, and the metres it drills before it is retired.
Frequently asked questions
How do you calculate drill bit cost per metre?
Add the bit’s purchase price to the total cost of its regrinds, then divide by the metres it drilled before it was scrapped. To include rig time, add the rig’s hourly operating cost divided by the bit’s penetration rate in metres per hour.
Is a more expensive drill bit worth it?
It is if it drills enough extra metres, or drills fast enough, to lower the total cost per metre. In the example above, a bit that costs 30% more but lasts 50% longer is about 17% cheaper per metre.
Should rig time be included in cost per metre?
Yes, when the bits drill at different speeds. Rig, fuel and crew costs are paid for every hour the rig runs, so a faster bit lowers the cost of each metre even if the bit itself costs more.
Why do my results change from one site to another?
Rock hardness and abrasiveness, air pressure, rig and operator all change bit life and penetration rate. Compare bits only on records from the same conditions.
ATR Drill supplies DTH, top hammer and tricone bits to drilling teams across the Middle East and Africa. To compare an ATR bit against the one you run now, send your bit size, rock type, rig and current metres per bit through the contact page or to sales@atrdrill.com.
