A compost thermometer is the simplest way to know whether your pile is actually working. Hot composting depends on microbes generating heat, and the temperature at the core tells you when the pile is active, when it is cooling and needs turning, when it is too hot, and when it is finished. The best compost thermometers have a long stainless steel stem that reaches the center of the pile, a sealed dial that will not fog in damp conditions, and a temperature range that covers at least 0 to 180°F. Stem length is the biggest choice: about 12 inches for tumblers and small bins, 20 inches for typical backyard piles, and 24 to 36 inches for large heaps. Below are seven compost thermometers currently listed on Amazon, compared on what each listing states, followed by a buyer’s guide and a temperature cheat sheet.
Part of our Composting & Soil guide →
In this guide
- 1. Reotemp 20 Inch Backyard Compost Thermometer — Best Overall for Backyard Piles
- 2. Reotemp Heavy Duty 36 Inch Compost Thermometer — Best for Large Heaps
- 3. Reotemp Heavy Duty 36 Inch With Probe Guard — Best for Dense or Woody Piles
- 4. Reotemp Backyard Pro 24 Inch — Best Mid-Length Option
- 5. Greenco 20 Inch Compost Soil Thermometer — Best Dual-Scale Value
- 6. VIVOSUN 20 Inch Compost Thermometer — Best Stated Accuracy
- 7. Reotemp K83B1 12 Inch Soil and Compost Thermometer — Best for Tumblers and Small Bins
- What to Look for in a Compost Thermometer
- Frequently Asked Questions
Disclosure: Urban Lotus Project is reader-supported. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.
How we compared: we compared 14 current Amazon listings on what each listing states (stem length and thickness, dial size and range, sealing and materials); we did not test or handle the products, and availability changes.
| Product | Best for | Key features | Buy |
|---|---|---|---|
| Reotemp 20 in Backyard | Best overall for backyard piles |
| Buy now →Check current price |
| Reotemp Heavy Duty 36 in | Best for large heaps |
| Buy now →Check current price |
| Reotemp Heavy Duty 36 in with Guard | Best for dense or woody piles |
| Buy now →Check current price |
| Reotemp Backyard Pro 24 in | Best mid-length option |
| Buy now →Check current price |
| Greenco 20 in Compost Thermometer | Best dual-scale value |
| Buy now →Check current price |
| VIVOSUN 20 in Compost Thermometer | Best stated accuracy |
| Buy now →Check current price |
| Reotemp K83B1 12 in | Best for tumblers and small bins |
| Buy now →Check current price |
Prices change often; check Amazon for today’s price. As an Amazon Associate we earn from qualifying purchases.
Key Takeaways
- Choose stem length by pile size: about 12 in for tumblers, 20 in for most backyard bins, 24–36 in for big heaps.
- A hermetically sealed dial prevents fogging, the most common failure in damp compost.
- Thicker stems (5/16 in) resist bending when pushed into dense material.
- An active hot pile typically runs about 130–160°F at the core.
- Check the core every few days and turn when it drops or climbs past about 160°F.
1. Reotemp 20 Inch Backyard Compost Thermometer — Best Overall for Backyard Piles
A 20 in stainless thermometer with a sealed Fahrenheit dial marked in three compost activity zones.
Check price on AmazonWhy We Like It
- 20 in stem suits most backyard bins
- Hermetically sealed dial resists fogging
- Three color zones read at a glance
- Compostable packaging and digital guide
| Specification | Details |
|---|---|
| Stem length | 20 in |
| Stem diameter | 1/4 in stainless steel |
| Scale | Fahrenheit with 3 activity zones |
| Dial | Hermetically sealed |
| Extras | Free digital composting guide |
| Temperature range | Not stated in listing |
Reotemp 20 in Backyard — compressed specs
A 20-inch stem reaches the center of most home compost bins and piles of about 3 by 3 feet, which is the size most often recommended for hot composting (our composting and soil guide covers pile building). Reotemp has the deepest presence on this shelf, with seven of the fourteen listings, and this Backyard model is its most straightforward option for beginners: stainless stem, a sealed dial so condensation does not hide the needle, and a dial marked in activity zones so you do not need to memorize temperature ranges.
The listing also notes the packaging is compostable and that a digital composting guide is included. Reotemp sells a 16-inch version of the same design if your bin is shallow. The 1/4-inch stem is lighter than the 5/16-inch heavy-duty models, so push it in gently in dense, woody material.
Pros
- Right length for typical bins
- Sealed, fog-resistant dial
- Beginner-friendly zones
Cons
- Fahrenheit only
- Thinner stem than heavy-duty models
- Range not stated in listing
Check Reotemp 20 in Backyard price on Amazon
2. Reotemp Heavy Duty 36 Inch Compost Thermometer — Best for Large Heaps
A 36 in, 5/16 in stainless stem with a large 3 in dual-scale dial reading 0 to 200 F.
Check price on AmazonWhy We Like It
- 36 in stem reaches the core of large piles
- Heavy 5/16 in stem
- Large 3 in Fahrenheit and Celsius dial
- Made in USA per listing
| Specification | Details |
|---|---|
| Stem length | 36 in |
| Stem diameter | 5/16 in stainless steel |
| Dial | 3 in, hermetically sealed |
| Range | 0 to 200°F and -10 to 90°C |
| Origin | Made in the USA |
| Weight | About 1.4 lb |
Reotemp Heavy Duty 36 in — compressed specs
Big windrows, manure piles and multi-bin systems hold heat deep inside, and a 20-inch probe may only read the cooler outer layer. This heavy-duty Reotemp has a full 36-inch stem with a thicker 5/16-inch diameter, so it resists bending when you push it into a large heap. The 3-inch dual-scale dial is the largest among the picks and easy to read while standing.
The 0 to 200°F range easily covers the hottest stages of composting. It is more thermometer than a small bin needs, and the long stem is awkward in tumblers, but for anyone composting at scale, it is the most capable option on the shelf.
Pros
- Longest reach on the shelf
- Sturdy heavy-duty stem
- Large dual-scale dial
Cons
- Too long for tumblers
- Heavier than backyard models
- No activity zones listed
Check Reotemp Heavy Duty 36 in price on Amazon
3. Reotemp Heavy Duty 36 Inch With Probe Guard — Best for Dense or Woody Piles
The heavy-duty 36 in Reotemp bundled with an extra steel guard that protects the stem.
Check price on AmazonWhy We Like It
- Steel probe guard protects the stem
- 36 in stainless stem
- 3 in sealed dual-scale dial
- Made in USA
| Specification | Details |
|---|---|
| Stem length | 36 in |
| Protection | Extra durable steel probe guard |
| Dial | 3 in, hermetically sealed |
| Range | 0 to 200°F and -10 to 90°C |
| Origin | Made in the USA |
| Stem diameter | Not stated in listing |
Reotemp Heavy Duty 36 in with Guard — compressed specs
This bundle pairs the same long Reotemp design with a steel guard around the stem. A guard is worth having if your piles include wood chips, stalks, straw or partially broken-down branches, where a probe can catch and bend, or if the thermometer will be pushed in repeatedly by several people on a farm or community garden site.
If your piles are mostly soft kitchen scraps and leaves, the guard adds little and the standard heavy-duty model above does the same job.
Pros
- Extra stem protection
- Long reach
- Clear dual-scale dial
Cons
- Overkill for small bins
- Bulkier to store
- Stem diameter not listed
Check Reotemp Heavy Duty 36 in with Guard price on Amazon
4. Reotemp Backyard Pro 24 Inch — Best Mid-Length Option
A 24 in, 5/16 in heavy-duty stem with a 2.5 in sealed dial and three activity zones from 0 to 200 F.
Check price on AmazonWhy We Like It
- 24 in stem for larger bins
- Heavy-duty 5/16 in stem
- Steady, Active and Hot zones
- PDF composting guide included
| Specification | Details |
|---|---|
| Stem length | 24 in |
| Stem diameter | 5/16 in stainless steel |
| Dial | 2.5 in, hermetically sealed |
| Scale | 0 to 200°F with 3 zones |
| Extras | PDF compost guide |
| Celsius scale | Not stated in listing |
Reotemp Backyard Pro 24 in — compressed specs
The Backyard Pro sits between the 20-inch beginner model and the 36-inch heavy-duty probes. Its 24-inch stem gives extra reach for 4-foot bins or piles that have grown taller than planned, and the thicker 5/16-inch stem makes it sturdier than the standard Backyard version. It keeps the color activity zones that make reading simple.
For many gardeners with a three-bin system or a pallet bin, this length is the most versatile choice. It is Fahrenheit only per the listing.
Pros
- Versatile length
- Thick, sturdy stem
- Easy-read zones
Cons
- Fahrenheit only
- Smaller dial than heavy-duty
- Long for tumblers
Check Reotemp Backyard Pro 24 in price on Amazon
5. Greenco 20 Inch Compost Soil Thermometer — Best Dual-Scale Value
A 20 in 304 stainless thermometer with a color-coded F and C dial, IP55 sealed lens and lifetime warranty.
Check price on AmazonWhy We Like It
- Fahrenheit and Celsius on one dial
- IP55 water-resistant sealed lens
- Reinforced welded dial joint
- Lifetime warranty stated
| Specification | Details |
|---|---|
| Stem length | 20 in |
| Stem diameter | About 0.2 in (5 mm), 304 stainless |
| Dial | 2 in, color-coded, 2-degree increments |
| Range | 40 to 180°F |
| Sealing | Hermetically sealed, IP55 |
| Warranty | Lifetime |
Greenco 20 in Compost Thermometer — compressed specs
Greenco’s thermometer is a good pick for anyone who wants both scales, since many composting guides and extension publications list temperatures in Celsius. The listing highlights a reinforced welded joint between dial and stem, often the weak point on cheaper probes, and an IP55-rated sealed lens.
Its 40 to 180°F range is narrower than the 0 to 200°F Reotemp and VIVOSUN models but still covers the useful composting band. The stem is slimmer than the heavy-duty Reotemps.
Pros
- Dual scale dial
- Reinforced joint
- Lifetime warranty
Cons
- Narrower range
- Slimmer stem
- Smaller dial than heavy-duty models
Check Greenco 20 in Compost Thermometer price on Amazon
6. VIVOSUN 20 Inch Compost Thermometer — Best Stated Accuracy
A 20 in 304 stainless probe with a 0 to 200 F dial, IP55 lens and stated accuracy of plus or minus 2 F.
Check price on AmazonWhy We Like It
- Accuracy of plus or minus 2°F stated
- Wide 0 to 200°F range
- Three colored activity zones
- IP55 sealed lens
| Specification | Details |
|---|---|
| Total length | 20 in (stem about 19.7 in) |
| Stem | 5 mm, 304 stainless steel |
| Dial | About 1.9 in |
| Range | 0 to 200°F |
| Accuracy | Plus or minus 2°F (stated) |
| Reading time | 3–5 minutes per listing |
VIVOSUN 20 in Compost Thermometer — compressed specs
VIVOSUN is the only listing among the picks that states an accuracy figure, plus or minus 2°F, and it gives practical instructions: insert into the pile and wait three to five minutes for the reading to settle. That patience applies to every dial thermometer and is worth remembering.
Its dial is slightly smaller than the Greenco and Reotemp 20-inch models, and the listing reads in Fahrenheit. It is a solid all-round choice for beginner composters with standard bins.
Pros
- Accuracy stated
- Wide range
- Clear usage guidance
Cons
- Smaller dial
- Slim stem
- Fahrenheit only per listing
Check VIVOSUN 20 in Compost Thermometer price on Amazon
7. Reotemp K83B1 12 Inch Soil and Compost Thermometer — Best for Tumblers and Small Bins
A 12 in thermometer for tumblers, small bins and soil, with a 32 to 178 F dual-scale dial.
Check price on AmazonWhy We Like It
- 12 in stem fits tumblers and small bins
- Fahrenheit and Celsius
- Waterproof, dust-proof stainless case
- Doubles as a soil thermometer
| Specification | Details |
|---|---|
| Stem length | 12 in |
| Range | 32 to 178°F, with Celsius |
| Case and bezel | 304 stainless steel |
| Lens | Glass; waterproof and dust-proof |
| Extras | Digital composting guide |
| Stem diameter | Not stated in listing |
Reotemp K83B1 12 in — compressed specs
Tumblers and small kitchen-scale bins do not need, and cannot fit, a 20-inch probe. The 12-inch K83B1 is sized for them, and it doubles as a soil thermometer for checking planting temperatures in spring. Thermometer World’s 12-inch dial model on the shelf is a similar alternative.
Short probes cannot reach the core of a full-size pile, so if you have both a tumbler and a bin, a 20-inch thermometer may serve both better.
Pros
- Right size for tumblers
- Dual scale
- Useful for soil too
Cons
- Too short for big piles
- Narrower top range
- No activity zones listed
Check Reotemp K83B1 12 in price on Amazon
What to Look for in a Compost Thermometer
Stem length
The probe needs to reach the center of the pile, where heat concentrates. As a rule, choose a stem at least half the width of your pile. Roughly: 12 inches for tumblers and small bins, 16 to 20 inches for standard 3-by-3-foot bins, 24 inches for larger bins, and 36 inches for big heaps and windrows. Short soil thermometers with 4- to 8-inch stems, which also appear on the shelf, are meant for garden soil and seed starting, not compost; for those, see our roundup of soil thermometers.
Stem thickness and construction
Stainless steel is standard. Thicker stems, such as 5/16 inch, resist bending in dense or woody material. A reinforced joint between dial and stem helps prevent the most common breakage point.
Dial, sealing and range
Compost is warm and humid, and unsealed dials fog quickly. Look for hermetically sealed or IP-rated dials. A range up to at least 180°F, ideally 200°F, covers every stage. Color-coded zones help beginners; dual Fahrenheit and Celsius scales help if you follow guides written in metric.
How to read your pile
| Core temperature | What it means | What to do |
|---|---|---|
| Below about 90°F | Cold or inactive pile | Add nitrogen-rich greens, moisten, turn |
| About 90–130°F | Active, moderate decomposition | Keep moist; turn when temperature falls |
| About 130–160°F | Hot composting range; kills many weed seeds and pathogens over time | Maintain; monitor every few days |
| Above about 160°F | Too hot; beneficial microbes slow | Turn to release heat and add air |
| Falls and stays low after turning | Curing or finished | Let cure, then screen and use |
A commonly cited target for reducing weed seeds and pathogens is holding the pile at 131°F or higher for several days, turning so all material spends time in the hot core. Our guides to hot vs cold composting and making compost faster explain how to get there.
Frequently Asked Questions
What temperature should my compost pile be?
An active hot pile typically runs about 130 to 160°F at the core. Below about 90°F, decomposition is slow; above 160°F, turn the pile to release heat and add oxygen.
How long should a compost thermometer stem be?
Long enough to reach the center of the pile: about 12 inches for tumblers, 16 to 20 inches for typical backyard bins, and 24 to 36 inches for large heaps.
Can I use a soil thermometer for compost?
Short soil thermometers cannot reach a pile’s core and may not read high enough. A 12-inch compost thermometer can double as a soil thermometer, but not the other way around for most piles.
How often should I check compost temperature?
Every two to three days during the active phase. Turn the pile when the temperature drops noticeably or climbs above about 160°F.
Can I leave a compost thermometer in the pile?
Many gardeners leave a sealed stainless thermometer in place during active composting, but remove it before turning so it is not bent, and store it dry over winter to extend its life.