HesapHanem

Screw Quantity Calculator

Enter the run length, screw spacing, rows and waste to estimate the screws you need.

How it is calculated

The tool counts screws per row, multiplies by the rows, then adds the waste allowance and rounds up: per row = floor(length ÷ spacing) + 1, then total = ceil(per row × rows × (1 + waste ÷ 100)). Length and spacing must use the same unit (the tool is written in centimetres, but any consistent unit gives the same count). The +1 is the extra screw at the start of the run, because screws are placed at both ends of each gap. The division is rounded down, so a leftover stretch shorter than one spacing gets no extra screw. If rows is empty or below 1 it counts as 1, and an empty waste counts as 0%.

Worked example

Fasten a 240 cm run with screws every 30 cm, in 2 rows, with 10% waste. Gaps along the run: 240 ÷ 30 = 8, so one row takes 8 + 1 = 9 screws. Two rows need 9 × 2 = 18 screws. With 10% extra: 18 × 1.10 = 19.8, rounded up to 20 screws to buy. If the spacing grows to 40 cm, the same run needs 7 screws per row instead of 9.

Try this example →

Common mistakes

  • Mixing units, such as a length in metres with a spacing in centimetres. A 2.4 m run entered as 2.4 with a 30 cm spacing gives a tiny count, so convert both to the same unit first.
  • Forgetting the screw at the start of the run. The count is gaps plus one, so a run of 240 and a spacing of 30 needs 9 screws per row, not 8.
  • Assuming a leftover piece is covered. If the length is not an exact multiple of the spacing, the last screw sits before the end, so check that the last screw is close enough to the edge.
  • Entering a decimal for the number of rows. Rows should be a whole number; the tool does not round it, so 2.7 rows gives a larger total than 2 rows.
  • Entering the waste as a fraction, such as 0.1 for 10%. The field takes a percentage, so 10 means 10%.

About this calculator

Fastening a run of material — a deck board, a stud wall, cabinet backing, or a sheet of drywall — needs a predictable number of screws to hold securely without over-fastening or running short mid-job. The count follows straightforward run-length math: screws per row = (run length ÷ spacing) + 1, multiplied by the number of parallel rows, then increased by a waste percentage to cover stripped heads, dropped screws, and mistakes.

This calculator takes the total run length, the spacing you want between fasteners, the number of rows, and a waste allowance, and returns how many screws to buy. Carpenters, deck builders, drywall installers, and DIY renovators use it before a materials run to a hardware store, since buying the wrong quantity of screws either wastes a trip or leaves a job half-finished.

Was this helpful?

You can pick up to 3 reactions.

Comments (1)

  • Editorial team

    The count is for one straight run, so for a deck or a plasterboard sheet, add each joist line or edge as a row rather than treating the whole area as one run. Check the last gap too: if the length is not an exact multiple of the spacing, the final screw ends up short of the end of the board. Do you fix into studs at set centres, and what spacing do you normally use?

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators