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Drip Faucet Calculator

Turn a dripping tap's drips per minute into the water wasted per day, month and year, in liters and gallons, and what it costs.

Level: Grades 6–7

Printable worksheet

Drip Faucet Calculator

Know the answer you need? Pick an input to work backward.

Inputs

Count the drops for one full minute, or for 15 seconds and multiply by 4.

To measure yours, catch drops in a measuring spoon or syringe and divide the volume by the count.

Use the volume charge from your water bill; add the sewer charge if it is billed by volume too.

Result

Water wasted per year

69.4 US gal

10 drips a minute wastes about 69.4 US gallons (262.8 L) a year, costing about $0.42.

Per year in liters
262.8 L
Per month (average)
5.79 US gal
Per month in liters
21.9 L
Per day
0.19 US gal
Per day in liters
0.72 L
Cost per year
$0.42
Cost per month
$0.03

See the step-by-step solution ↓

Step-by-step solution

  1. Water lost per minute = drips per minute × drop volume

    10×0.05 mL=0.5 mL

  2. Scale up to a full day: multiply by the 1,440 minutes in a day, then turn mL into liters

    0.5 mL×1,4401,000=0.72 L

  3. Multiply the daily loss by 365 to see the total over a whole year

    0.72 L×365=262.8 L

  4. Convert to US gallons (1 US gal = 3.785411784 L)

    262.8 L3.785411784=69.424 US gal

  5. Yearly cost = liters ÷ liters per billing unit (1,000 US gal = 3,785.411784 L) × price

    262.83,785.411784×$6.00=$0.42

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

See how much water and money a dripping tap wastes in a day, a month and a year. A single drip looks harmless, but a tap that drips all day, every day, adds up. The total depends on just two numbers: how often a drop falls and how big each drop is. Multiply them and you have a flow rate (how much water leaks each minute). From there you can scale up to a day, a month or a year.

This calculator does that scaling and shows the result in both liters and US gallons. It also puts a price on it, using the water rate from your own bill. It's a quick way to decide whether a new washer or cartridge is worth fitting today.

Where it's used

Why this math matters outside the classroom:

  • Home repairs. Homeowners see that 10 drips a minute at 0.05 mL each wastes 720 mL a day, a reason to replace a worn washer.
  • Yearly totals. Students scale a daily waste of 1 L to 365 L a year, close to 96 US gallons.
  • Water campaigns. Water utilities use drip estimates in conservation campaigns to show how small leaks add up.
  • Rental properties. Property managers compare a year of dripping water's cost with the price of a plumber's visit.

Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.RP.A.3.b, 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Count the drops falling from the tap for one minute and enter the number.
  2. Keep the approximate drop volume of 0.05 mL, or measure your own drops and enter that instead.
  3. If several taps drip at about the same rate, enter how many.
  4. Enter the water price from your bill and choose its billing unit. Read the yearly, monthly and daily waste and the cost.

What the inputs mean

Drips per minute
Counting for a full minute is most accurate. Fast drips are easier to count over 15 seconds, then multiply by 4. A steady trickle is no longer dripping, and this calculator isn't meant for that.
Volume of one drop (common approximation: 0.05 mL)
0.05 mL (20 drops per milliliter) is a common approximation. Real drops vary with the faucet's outlet and the water's surface tension (the slight 'skin' that holds a drop together). To measure yours, let the tap drip into a kitchen measuring spoon and count the drops until it's full. Then divide the spoon's volume by the count. A US teaspoon is about 4.93 mL.
Water price (example: $6 per 1,000 gal)
Water bills usually show a volume charge per 1,000 gallons, per 100 cubic feet (often written CCF or HCF), or per cubic meter. If sewer charges are also billed on the water you use, add that rate too. The $6 per 1,000 gallons default is only an example.

Formula and method

flow (mL/min) = drips per minute × drop volume × faucets
daily volume (L) = flow × 1,440 ÷ 1,000
yearly volume (L) = daily volume × 365
monthly volume = yearly volume ÷ 12
US gallons = liters ÷ 3.785411784
yearly cost = yearly liters ÷ liters per billing unit × price

Flow is how much water leaks each minute, in milliliters (mL). A day has 1,440 minutes, and dividing milliliters by 1,000 gives liters (L). The year is taken as 365 days, and a month as an average twelfth of a year (about 30.4 days).

One US gallon is exactly 3.785411784 liters. The billing units convert exactly too: 1,000 US gallons is 3,785.411784 L, 100 cubic feet is 2,831.6846592 L, and a cubic meter is 1,000 L.

Worked example

A bathroom tap drips 10 times a minute. The drops are assumed to be 0.05 mL each, and water costs an example $6 per 1,000 US gallons.

  1. Flow: 10 × 0.05 mL = 0.5 mL per minute.
  2. Per day: 0.5 × 1,440 ÷ 1,000 = 0.72 L.
  3. Per year: 0.72 × 365 = 262.8 L, and 262.8 ÷ 3.785411784 = 69.42 US gallons.
  4. Per month: 262.8 ÷ 12 = 21.9 L, or about 5.79 US gallons.
  5. Cost: 262.8 ÷ 3,785.411784 × $6 = $0.42 a year.

Result: A 10-drip-per-minute leak wastes about 69.4 US gallons (262.8 L) a year. At $6 per 1,000 gallons that is only about 42 cents, but the waste grows quickly with faster drips.

Understanding the result

Cost is often small for a slow drip, because household water is cheap per liter. The volume is the better measure of waste. And if the leak is hot water, it wastes the energy used to heat it too.

The total scales directly with the drip rate. A tap dripping once a second (60 per minute) wastes six times the default example. A leak that has become a thin stream can waste many times more.

To judge how urgent the repair is, compare the yearly figure with everyday uses of water. A bath or a load of laundry makes a handy yardstick.

Assumptions and limitations

  • The drip rate stays constant around the clock and all year.
  • Every drop has the same volume.
  • The water price is a flat rate per unit with no tiers, fixed charges or taxes.
  • Drop volume is the largest source of uncertainty. The default is an approximation, so a measured value gives a much better estimate.
  • The cost of hot water heating is not included.
  • Leaks inside walls, toilets that run, and irrigation leaks need a meter test, not a drip count.

Frequently asked questions

How big is one drop of water?

It depends on the opening it falls from. Values from about 0.03 to 0.1 mL are common, and 0.05 mL is a convenient approximation. Measuring your own drops with a spoon or syringe is easy and makes the result much more reliable.

Is a dripping tap worth fixing?

Usually yes. The parts are often inexpensive, and a slow drip tends to get worse over time as the washer or seal wears further. If the drip is hot water, fixing it also stops heating water that goes straight down the drain.

How do I find my water price?

Look for the volume or consumption charge on your water bill. It's quoted per 1,000 gallons, per 100 cubic feet, or per cubic meter. Ignore fixed monthly service fees, which you pay whether or not the tap drips.

Why does the monthly figure use one twelfth of a year?

Months have 28 to 31 days, so an average month (365 ÷ 12, about 30.4 days) gives a figure that adds up exactly to the yearly total.

How this calculator is checked

Method: Direct rate × time scaling; exact volume definitions (US gallon = 3.785411784 L; ft³ = 28.316846592 L). The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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