Tap Fill Time Calculator
Knowing how long a basin, sink or bath will take to fill helps you plan bath time, avoid overflows, and judge whether a new tap or mixer is worth the upgrade. Enter the volume you need to fill and your tap's flow rate below.
Work out how long your tap takes to fill
Enter the volume you need to fill and your tap's flow rate.
A standard bath holds roughly 80L.
Basin taps are usually 4-8 L/min, bath taps 10-20 L/min.
At this flow rate, filling 80L will take approximately:
6 min 40 sec
A lower flow rate means a longer fill time but can also mean lower water pressure demand on your plumbing.
Recommended products
A few well-reviewed taps and mixers to consider.
- 5 Years
£36.99
Pros
- GROHE 28mm ceramic cartridge for smooth control
- Water-saving technology
- Single-lever, one-hole installation
Cons
- No waste set included
£54.45
Pros
- Clicker waste included, no extra purchase needed
- Chrome-plated finish
- Simple mono installation
Cons
- Basic styling compared to premium ranges
- 1 Year
£24.99
Pros
- Budget-friendly pair of hot and cold taps
- Simple compression fitting for quick swaps
Cons
- No mixed-temperature flow
- Ceramic disc washers wear faster than premium taps
Frequently asked questions
Why does my bath take so much longer to fill than my basin?
It comes down to both volume and flow rate — a bath needs roughly 80L compared to a basin's 5-10L, and while bath taps usually flow faster too, the much larger volume still means a noticeably longer fill time.
What is a typical flow rate for a UK bathroom tap?
Basin taps are usually 4-8 litres per minute, while dedicated bath taps or bath fillers tend to run at 10-20 litres per minute, so checking which type you have will make this estimate more accurate.
Does low water pressure affect my fill time estimate?
Yes — the flow rate figures here assume typical UK mains pressure, so if your home has low pressure or a small combi boiler, your actual flow rate (and therefore fill time) could be lower than the tap's rated maximum.
Can I speed up filling a bath without changing my tap?
Fitting a bath filler or upgrading to a wider-bore tap can increase flow rate, but the simplest fix is often just running both hot and cold taps together rather than one at a time, which combines their flow rates.
How this calculator works
The calculator uses the formula: Fill Time (minutes) = Basin Volume (litres) / Tap Flow Rate (litres per minute). It’s a straightforward calculation, but it relies on an accurate understanding of your tap's flow rate. Most modern taps have a flow regulator, and manufacturers often specify this in litres per minute at various pressures – we assume standard mains water pressure for our calculations.
The calculator takes the volume of the basin or bath (in litres) as input from you. Then, it divides this by your specified tap flow rate (entered in LPM). The result is the estimated fill time in minutes. Remember that variations in water pressure and tap condition can slightly affect the actual filling time; this provides a close approximation.
Tap Flow Rates – A Quick Reference
- **Low-Flow Taps:** Many modern taps now have flow restrictors set to 6-8 litres per minute (lpm). These are designed to conserve water and can significantly impact fill times, especially for larger basins.
- **Standard Taps:** Older or standard taps often have a flow rate of around 10-12 litres per minute (lpm). This is a common range for many UK households.
- **High-Pressure Taps:** Some taps, particularly those installed in older properties with higher water pressure, can achieve flow rates of up to 15-18 litres per minute (lpm). However, this increased flow also consumes more energy and water.
- **Check your tap’s label:** Many modern taps will have a marked flow rate setting. Ensure you select the correct LPM for accurate calculations – typically found in the tap’s technical specifications.
- **Water Pressure Variations:** Water pressure can vary depending on the time of day, especially during peak usage periods. This can affect the actual flow rate, so consider this when using the calculator.
Worked example: Filling a 400 Litre Bath
Let’s say you have a bath with a capacity of 400 litres and you're using a tap with a flow rate of 12 litres per minute (lpm). Using the calculator, we get: Fill Time = 400 / 12 = 33.33 minutes. This means it will take approximately 33 minutes and 20 seconds to fill your bath fully at this flow rate.
Assuming a standard mains water pressure of 5 bar (a common UK value), the tap’s flow rate should be relatively consistent. However, if you're experiencing fluctuations in your water pressure, such as during peak times when many households are using hot water simultaneously, the fill time could extend slightly. At £9.00 per kWh for average UK domestic electricity rates, a 33-minute bath will cost approximately £2.70 to heat.
More questions answered
What if my tap doesn’t have a flow rate listed?
If your tap doesn't have a specified flow rate, you can estimate it by timing how long it takes to fill a smaller container (e.g., a 5-litre jug) and then calculating the litres per minute. A good starting point would be around 8-10 LPM for a standard tap.
How does water pressure affect the calculation?
Higher water pressure will result in a faster flow rate, leading to a shorter fill time. Conversely, lower water pressure will increase the fill time. While we assume standard mains pressure, fluctuations can impact the accuracy.
What if I’m using a shower mixer tap?
Shower mixer taps often have multiple flow settings. Ensure you select the appropriate LPM setting for the calculator to provide an accurate result – typically, use the lowest flow rate setting for filling a bath or basin.
Can I use this calculator for sinks?
Yes! The formula applies equally well to sinks. Just input the sink's volume in litres and your tap’s LPM flow rate. Smaller sinks will naturally require shorter fill times.
What is ‘litres per minute (LPM)?’,
LPM stands for Litres Per Minute, which measures the volume of water flowing through your tap in one minute. It’s a crucial unit for this calculator – check your tap’s specifications to determine its LPM value.
I entered the wrong basin volume; will the result still be accurate?
The accuracy of the result is directly dependent on the accuracy of the input basin volume. Ensure you're entering the correct volume in litres – double-check your measurements!
Can I use this calculator to estimate shower fill times?
While possible, it’s less precise for showers due to varying flow rates and multiple spray patterns. Use a lower flow rate setting on the mixer tap for a more accurate estimate.
What if my tap is old and leaking?
A leaking tap will significantly reduce its flow rate, increasing the fill time considerably. Consider having your tap inspected and repaired by a qualified plumber to ensure optimal performance.
Does this calculator account for warm water?
The calculator assumes you're filling with warm water, as most households heat their water to around 60-70°C. Filling with cold water will naturally take longer than filling with warm water.
How does the size of the bath/basin affect the results?
Larger baths and basins require significantly more litres to fill, directly impacting the calculated fill time. Always ensure you’re using the correct volume measurement for your specific basin or bath size.