20 Gallon Long Tank - Grower Calc

20 gallon long - popular for breeding and community tanks - Net nutrient solution volume for hydro systems.

What shape is your reservoir-

Enter your reservoir dimensions

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Results

US Gallons
40.4 US Gallons
(153 Liters)
Gross reservoir volume: 44.9 gal (170 L)
Use net solution volume (40.4 gal) for nutrients, EC, and pH adjustments.
Solution weight: 337 lbs (153 kg)
Estimated full system weight: 377 lbs (171 kg)
Includes solution, media estimate, and reservoir tare

Recommended For Your Reservoir · ~40 gal reservoir · 40W heater estimate

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Verify results before use. See our disclaimer.

Rough equipment hints

Heater / chiller load
~40 W
2 °F lift · 40.4 gal net
Recirculation pump band
40-121 GPH
1–3× turnover/hr · compare to pump curve at actual head
Drain-down volume
8.1 gal
20% of net · adjust in Advanced

Popular reservoir presets

10 Gallon40 Gallon Breeder50 Gallon1 Foot1.5 Feet2 Feet30cm Cube32cm CubeCurved-front reservoir (preset)Round stock tank (preset)2ft by 1ft

Quick links to pre-filled dimensions-always verify inside measurements on your actual vessel.

20 Gallon Long Tank - reservoir volume

This preset matches a 20.0 gal (~76 L) nominal size. Use it as a starting point for DWC, NFT, Dutch bucket, or other layouts that use a reservoir near this capacity.

Verify inside dimensions on your actual vessel-plastic totes and stock tanks often differ from the label. Then tune fill height and displacement so nutrient math matches real solution volume.

How to use this calculator

  • Dimensions are pre-filled for this nominal gallon size
  • Confirm inside length, width, and depth on your actual reservoir or tote
  • Adjust fill height to the normal operating level (not the overflow edge)
  • Add displacement if roots, media, or hardware sit below the waterline
  • Use net gallons or liters for every nutrient, acid, or peroxide calculation

Cooling & larger vessels

Chillers and stock-style reservoir picks

~40 gal reservoir · 40W heater estimate

Water chillers

Helpful when ambient heat makes root-zone temperature drift upward.

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How to measure your container

What You Need

  • Measuring tape or ruler
  • Paper and pen to write down measurements

Why Accurate Measurements Matter

Knowing your exact reservoir dimensions is essential for calculating working solution volume, which affects:

  • Nutrient dosing and concentrate mixing
  • EC and pH adjustment accuracy
  • Pump turnover and recirculation planning
  • Heater or chiller sizing
  • Drain-down and reservoir change planning

Common Mistakes to Avoid

Measuring the outside: Always measure the inside water-holding area, not the outside wall or rim.

Ignoring displacement: Root mass, rafts, media, manifolds, and hardware all reduce working solution volume.

Mixing units: Do not switch between inches and centimeters mid measurement.

Measuring to the top: Reservoirs are rarely run brim-full. Measure actual operating solution height, not the outer wall height.

Different Tank Types

Curved-front reservoirs: Measure the straight back panel. The calculator accounts for the bowed face.

Round tanks: Measure the inside diameter (straight line across the widest part) and fill depth.

Corner sumps: Measure the longest straight edges on each side.

Measuring Steps

1. Length

Measure from left to right across the inside of the reservoir. This is the longest straight side in front view.

2. Width

Measure from front to back across the inside. This is the reservoir depth.

3. Height

Measure from the bottom to the normal solution line on the inside of the reservoir. Do not include lids, rims, or freeboard above the operating level.

Quick Reference

Standard notation:

Length × Width × Height

Example: 36 × 18 × 16 inches

Tools That Work Best

  • Metal measuring tape (most accurate)
  • Cloth tape for curved tanks
  • Ruler for small tanks under 10 gallons
  • Smartphone apps with AR measurement

Important Tips

  • Measure inside the reservoir: Do not include wall thickness, lids, or top lips. Measure the actual solution-holding area.
  • Measure in inches or centimeters: Most tape measures show both. Pick one unit and stick with it for all three measurements.
  • Round to the nearest whole number: You do not need perfect precision. Rounding to the nearest inch or centimeter is fine.
  • Write it down: Length × Width × Height. For example: 36 × 18 × 16 inches.
Pro tip: If your reservoir has a molded lip, baffles, or a float-controlled operating line, measure where the solution actually sits during normal use.

Hydroponics reservoir volume: gross vs net, nutrients, and common mistakes

A reservoir label is marketing; your plants swim in net solution volume-the liters or gallons below the normal waterline minus roots, media, and hardware. That number drives EC, pH adjustments, batch concentrates, sanitizer dilution, and how fast your pump truly turns the tank over.

Treat this page as your baseline, then validate with a tape inside the bin or a metered fill when you commission a new bay. Update after swaps of rafts, chillers, or manifold layouts because each steals a different slice of displacement.

How to use gross vs net on the results card

Gross volume is the empty cavity to your entered fill height. Net volume applies your displacement slider-think hydroton, perlite, net cups, UV sleeves, and horizontal pump bodies. Nutrient math should track net; structural checks should include the full mass of liquid plus equipment.

  • Use net liters or gallons on feed charts, peroxide flushes, acid/base additions, and microbial inoculants.
  • Use gross only when comparing nominal tote sizes or checking if a mold will physically fit a footprint.
  • When in doubt on nutrients, round net volume down slightly-underfeeding is easier to correct than a burned crop from overdosing.

Good reminder

Bottle labels and spreadsheets assume the volume you type is real solution in the reservoir-not the sticker on the side of an IBC.

Why nominal sizes lie

Rotomolded reservoirs taper, IBC totes have cage gaps, and stock tanks bow when full. Catalog depth often ignores float valve standpipes or anti-vortex screens. The percent error is tiny in a 10,000 L farm tank but huge in a 40 L cloner where one liter shifts EC fast.

  • Measure at the operating level you actually hold with pumps running.
  • Account for return lines that drain back into the same reservoir on pump-off events.
  • If multiple tanks share one chemistry loop, dose for the combined working volume they share.

Tasks that demand honest volume

  • Mixing two-part or three-part concentrates into topping barrels.
  • Shock dosing peroxide or hypochlorite for biofilm control (always follow label + crop restrictions).
  • Sizing backup aeration or circulation when a pump fails mid-shift.
  • Checking whether a chiller or heat exchanger has enough thermal mass for peak greenhouse loads.

Percent changes and drain-downs

Replacing “20% of the reservoir” means 20% of the working solution, not 20% of the catalog height. If you underestimate volume, the same bucket pull is a bigger concentration swing than you planned-watch young plants and freshly transplanted roots first.

Equipment hints on this page

Heating watts and GPH bands are rules of thumb tied to net gallons. Compare them to manufacturer pump curves, actual head pressure, and your climate-not as a substitute for engineering on large farms.

Shapes and tricky vessels

Curved-front totes, round stock tanks, and corner sumps need the matching geometry mode. When a shape is truly odd, measure in sections or default to a conservative rectangle-then confirm with a physical fill test before locking a recipe.

When to rerun the calculator

Any time fill height, displacement, or connected volume changes: new chiller bundle, deeper raft, added UV, second pump manifold, or switching between summer and winter operating levels. Log the net volume beside the date on your nutrient sheet so the whole crew uses the same figure.